WO2018116652A1

WO2018116652A1 - Electrolyte solution, electrochemical device, lithium ion secondary battery, and module

Info

Publication number: WO2018116652A1
Application number: PCT/JP2017/039591
Authority: WO
Inventors: 謙三高橋; 坂田　英郎; 穣輝山崎; 博之有馬; 雅量木下; 木下　信一
Original assignee: ダイキン工業株式会社
Priority date: 2016-12-22
Filing date: 2017-11-01
Publication date: 2018-06-28

Abstract

Provided is an electrolyte solution which enables the achievement of a module or an electrochemical device such as a lithium ion secondary battery that has a high residual capacity retention rate after storage at high temperatures. This electrolyte solution is characterized by containing an acid anhydride (1) represented by general formula (1). In the formula, ring A represents a saturated or unsaturated hydrocarbon ring having 3-8 carbon atoms or a saturated or unsaturated heterocyclic ring having 3-8 carbon atoms; and ring A may have a substituent, while being monocyclic or polycyclic.

Description

Electrolytic solution, electrochemical device, lithium ion secondary battery, and module

The present invention relates to an electrolytic solution, an electrochemical device, a lithium ion secondary battery, and a module.

With the recent reduction in weight and size of electrical products, development of lithium-ion secondary batteries having high energy density is in progress. Further, as the application field of lithium ion secondary batteries expands, improvement of battery characteristics is desired. In particular, when lithium ion secondary batteries are used in vehicles, the battery characteristics will become increasingly important.

In Patent Document 1, in a lithium secondary battery having a battery element containing an electrolyte layer having a non-fluidic electrolyte at a contact portion between at least one of a positive electrode and a negative electrode, the electrolyte layer contains an acid anhydride. A lithium secondary battery is described.

Japanese Patent Laid-Open No. 2001-155572

However, an electrolyte solution having a high residual capacity retention rate after being stored at a high temperature is required.

An object of the present invention is to provide an electrolytic solution capable of obtaining an electrochemical device or module such as a lithium ion secondary battery having a high remaining capacity retention rate after storage at high temperature.

The present invention relates to a general formula (1):

(In the formula, ring A is a saturated or unsaturated hydrocarbon ring having 3 to 8 carbon atoms, or a saturated or unsaturated heterocyclic ring having 3 to 8 carbon atoms, which may have a substituent. , Which may be monocyclic or polycyclic), an electrolyte solution characterized by containing an acid anhydride (1).

The electrolytic solution preferably contains 0.001 to 5% by mass of the acid anhydride (1) with respect to the electrolytic solution.

The electrolytic solution further contains a solvent, and the solvent has the general formula (2):

(Wherein Rf ²¹ is —F, —CHF ₂ or —CF ₃ , R ²¹ , R ²⁴ and R ²⁵ are the same or different, and —H, —F, —CH ₃ , —CHF ₂ or —CF ₃ , R ^22, and R ²³ are the same or different, and —H, —F, —CH ₃ , —CHF _2, or —CF ₃ , or any one of R ²³ and the carbon atom to which R ²² is bonded to R ²³ It is preferable to include a fluorinated carbonate (2) represented by a single bond that forms a ring by bonding to bonded carbon atoms.

The present invention is also an electrochemical device comprising the above-described electrolytic solution.

The present invention is also a lithium ion secondary battery comprising the above electrolyte solution.

The present invention is also a module comprising the electrochemical device or the lithium ion secondary battery.

According to the electrolytic solution of the present invention, an electrochemical device or module such as a lithium ion secondary battery having a high remaining capacity retention rate after being stored at a high temperature can be obtained.

Hereinafter, the present invention will be specifically described.

The electrolytic solution of the present invention has the general formula (1):

(In the formula, ring A is a saturated or unsaturated hydrocarbon ring having 3 to 8 carbon atoms, or a saturated or unsaturated heterocyclic ring having 3 to 8 carbon atoms, which may have a substituent. , Which may be monocyclic or polycyclic), and an acid anhydride (1).

Ring A may have one or more substituents. Examples of the substituent include —F, a non-fluorinated alkyl group, a fluorinated alkyl group, and an alkoxy group. Among them, —F, —CH ₃ , —CH ₂ F, —CF ₂ H, —CF ₃ And at least one selected from the group consisting of —OR (R is an alkyl group having 1 to 5 carbon atoms), and is selected from the group consisting of —F, —CH ₃ , —CH ₂ F and —CF _3. At least one is more preferable. The number of substituents is preferably 1 or 2.

Ring A is preferably a 3- to 6-membered monocycle or a polycycle containing a 3- to 6-membered monocycle, more preferably a 3- to 4-membered monocycle, and even more preferably a 3-membered monocycle.

The polycycle may be a condensed ring, a bridged ring or a spiro ring, and a bridged ring is preferred. Examples of the bridged ring include a bicyclic ring in which a 6-membered ring is bridged by —CH ₂ —, —CH═CH—, —O— or the like.

As the acid anhydride (1), any of the following compounds is preferable. You may use 2 or more types as an acid anhydride (1).

As the acid anhydride (1), a higher residual capacity retention ratio can be obtained, and among these, any of the following compounds is more preferable.

As the acid anhydride (1), since a higher residual capacity retention ratio can be obtained, among them, any of the following is more preferable.

As the acid anhydride (1), the following is particularly preferable because a higher residual capacity retention ratio can be obtained.

The electrolyte solution of the present invention preferably contains 0.001 to 5% by mass of the acid anhydride (1) with respect to the electrolyte solution because a higher residual capacity retention rate can be obtained. As content of acid anhydride (1), 0.01 mass% or more is more preferable with respect to electrolyte solution, 0.1 mass% or more is further more preferable, 3 mass% or less is more preferable, and 2 mass% or less. Is more preferable.

The electrolytic solution of the present invention preferably contains a solvent.
The content of the solvent is preferably 95% by mass or more, more preferably 97% by mass or more, still more preferably 98% by mass or more, preferably 99.999% by mass or less, and 99.990% by mass with respect to the electrolytic solution. The following is more preferable, and 99.900 mass% or less is still more preferable.

The solvent preferably contains carbonate.
The solvent preferably contains a cyclic carbonate and a 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 a non-fluorinated saturated cyclic carbonate, a fluorinated saturated cyclic carbonate, a fluorinated chain carbonate, and a non-fluorinated chain carbonate. Among these, it is more preferable to include at least one selected from the group consisting of a fluorinated saturated cyclic carbonate and a fluorinated chain carbonate, and it is even more preferable to include a fluorinated saturated cyclic carbonate.
The solvent is preferably a non-aqueous solvent, and the electrolytic solution of the present invention is preferably a non-aqueous electrolytic solution.

Examples of the non-fluorinated saturated cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate.

Among these, as the non-fluorinated saturated cyclic carbonate, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, and butylene carbonate is preferable in that the dielectric constant is high and the viscosity is suitable.
As said non-fluorinated saturated cyclic carbonate, 1 type of the compound mentioned above may be used, and 2 or more types may be used together.

The content of the non-fluorinated saturated cyclic carbonate is preferably 0 to 99% by volume, more preferably 1% by volume or more, and more preferably 90% by volume or less based on the solvent.

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

(Wherein X ¹ to X ⁴ are the same or different and each represents —H, —CH ₃ , —C ₂ H ₅ , —F, a fluorinated alkyl group optionally having an ether bond, or an ether bond. Represents a fluorinated alkoxy group which may have, provided that at least one of X ¹ to X ⁴ has —F, a fluorinated alkyl group which may have an ether bond, or an ether bond; It is a good fluorinated alkoxy group.).
When the fluorinated saturated cyclic carbonate is contained, when the electrolytic solution of the present invention is applied to a lithium ion secondary battery or the like, a stable film can be formed on the negative electrode, and the side reaction of the electrolytic solution at the negative electrode is sufficient. Can be suppressed. As a result, extremely stable and excellent charge / discharge characteristics can be obtained.
In the present specification, the “ether bond” is a bond represented by —O—.

From the viewpoint of good dielectric constant and oxidation resistance, one or two of X ¹ to X ⁴ may have —F, a fluorinated alkyl group that may have an ether bond, or an ether bond. A fluorinated alkoxy group is preferred.

X ¹ to X ⁴ represent —H, —F, a fluorinated alkyl group (a), an ether bond, because a decrease in viscosity at a low temperature, an increase in flash point, and an improvement in solubility of the electrolyte salt can be expected. The fluorinated alkyl group (b) or the fluorinated alkoxy group (c) is preferable.

The fluorinated alkyl group (a) is obtained by substituting at least one hydrogen atom of the alkyl group with a fluorine atom. The number of carbon atoms in the fluorinated alkyl group (a) is preferably 1-20, more preferably 2-17, still more preferably 2-7, and particularly preferably 2-5.
If the carbon number is too large, the low-temperature characteristics may be lowered or the solubility of the electrolyte salt may be lowered. If the carbon number is too small, the solubility of the electrolyte salt is lowered, the discharge efficiency is lowered, and further, An increase in viscosity may be observed.

Among the fluorinated alkyl groups (a), those having 1 carbon atom include CFH ₂ —, CF ₂ H—, and CF ₃ —. In particular, CF ₂ H— and CF ₃ — are preferable for high temperature storage characteristics.

Among the fluorinated alkyl groups (a), those having 2 or more carbon atoms are represented by the following general formula (a-1):
R ¹ -R ^2- (a-1)
(Wherein 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; provided that R ¹ and A fluorinated alkyl 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.
R ¹ and R ² may further have other atoms other than the carbon atom, the hydrogen atom, and the fluorine atom.

R ¹ is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. R ¹ is preferably a linear or branched alkyl group having 1 to 16 carbon atoms. The number of carbon atoms of R ¹ is more preferably 1 to 6, and further 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 —,

Etc.

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 C F 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 Is mentioned.

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

Etc. are preferable. However, since the viscosity tends to increase when the branch has CH ₃ -or CF _3- , the number is preferably small (one) 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 minimum 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 minimum structural unit:

In addition, among the above examples, it is preferable that the base is composed of a constitutional unit that does not contain Cl, because de-HCl reaction with a base does not occur and is more stable.

When R ² is linear, it is composed of only the above-mentioned linear minimum structural unit, and —CH ₂ —, —CH ₂ CH ₂ — or —CF ₂ — is particularly preferable. From the viewpoint of further improving the solubility of the electrolyte salt, —CH ₂ — or —CH ₂ CH ₂ — is more preferable.

When R ² is branched, it comprises at least one of the aforementioned branched minimum structural units, and R ² is represented by 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, provided that when X ^b is CF ₃ , X ^a is H or CH ₃ . In particular, the solubility of the electrolyte salt can be further improved.

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

Etc.

The fluorinated alkyl group (b) having an ether bond is obtained by substituting at least one hydrogen atom of the alkyl group having an ether bond 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 increases, and the fluorine-containing group increases, so that the solubility of the electrolyte salt decreases due to a decrease in the dielectric constant, and compatibility with other solvents. Decrease may be observed. From this viewpoint, the fluorinated alkyl group (b) having an ether bond preferably has 2 to 10 carbon atoms, and more preferably 2 to 7 carbon atoms.

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 minimum structural unit constituting such a linear or branched alkylene group is shown below.

(Ii) Branched minimum structural unit:

The alkylene group may be composed of these minimum structural units alone, and may be linear (i), branched (ii), or linear (i) and branched (ii). You may comprise by the combination. Preferred specific examples will be described later.

As a more preferred fluorinated alkyl group (b) having an ether bond, the general formula (b-1):
R ^3- (OR ⁴ ) _n1- (b-1)
(Wherein 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) N1 is an integer of 1 to 3; provided that at least one of R ³ and R ⁴ has a fluorine atom).

Examples of R ³ and R ⁴ include the following, and these can be combined as appropriate to form a fluorinated alkyl group (b) having an ether bond represented by the general formula (b-1). However, it is not limited to these.

(1) As R ³ , the general formula: X ^c ₃ C— (R ⁵ ) _n2 — (the three X ^c are the same or different and each is H or F; R ⁵ represents a fluorine atom having 1 to 5 carbon atoms) An alkylene group which may have; n2 is preferably an alkyl group represented by 0 or 1).

When n2 is 0, R ³ includes CH ₃ —, CF ₃ —, HCF ₂ —, and H ₂ CF—.

As a specific example when n2 is 1, 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 _{_{_{_{H 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 -, C _{_{_{_{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 Examples thereof include _2- , CH ₃ CF ₂ CH ₂ CF ₂ 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 — and the like.

n2 is 1, and as R ³ is branched, the

Etc.

However, since having a branch such as CH ₃ — or CF ₃ — tends to increase in viscosity, R ³ is more preferably linear.

(2) In — (OR ⁴ ) _n1 — in the 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.

Preferable specific examples of R ⁴ include the following linear or branched ones.

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 — and the like can be exemplified.

As a branched chain,

Etc.

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) is represented by the general formula: X ^d ₃ C— (R ⁶ ) _n3 —O— (the three X ^d are the same or different, and all are H or F; R ⁶ is preferably carbon number) A fluorinated alkoxy group represented by an alkylene group optionally having 1 to 5 fluorine atoms; n3 is 0 or 1; provided that any one of three X ^d contains a fluorine atom is particularly preferable.

Specific examples of the fluorinated alkoxy group (c) include a fluorinated alkoxy group in which an oxygen atom is bonded to the terminal of the alkyl group exemplified as R ¹ in the general formula (a-1).

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 temperatures and the effect of increasing 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 based on {(number of fluorine atoms) based on the structural formula of each group. × 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, and 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 {(number of fluorine atoms × 19) / molecular weight of 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 the fluorinated saturated cyclic carbonate in which at least one of X ¹ to X ⁴ is —F,

Etc. These compounds have a high withstand voltage and good solubility of the electrolyte salt.

other,

Etc. can also be used.

Specific examples 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 are:

Etc.

Specific examples of fluorinated saturated cyclic carbonates 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,

Etc.

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

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

The fluorinated saturated cyclic carbonate is not limited to the specific examples described above. Moreover, the said fluorinated saturated cyclic carbonate may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

The content of the fluorinated saturated cyclic carbonate is preferably 0 to 99% by volume in the solvent, more preferably 1% by volume or more, further preferably 5% by volume or more, more preferably 95% by volume or less, and 90% by volume. % Or less is more preferable.

As said fluorinated chain carbonate, general formula (B):
Rf ² OCOOR ⁶ (B)
(Wherein Rf ² is a fluorinated alkyl group having 1 to 7 carbon atoms, and R ⁶ is an alkyl group optionally containing a fluorine atom having 1 to 7 carbon atoms). Can be mentioned.

The electrolyte solution of the present invention preferably contains the fluorinated chain carbonate in that 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 that may contain a fluorine atom having 1 to 7 carbon atoms.
The 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, more preferably 2 to 4 in view of low viscosity.
If the carbon number is too large, the low-temperature characteristics may be lowered or the solubility of the electrolyte salt may be lowered. If the carbon number is too small, the solubility of the electrolyte salt is lowered, the discharge efficiency is lowered, and further, An increase in viscosity may be observed.

Examples of the fluorinated alkyl group having 1 carbon atom include CFH ₂ —, CF ₂ H—, and CF ₃ —. In particular, CF ₂ H— and CF ₃ — are preferable for 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)
(Wherein 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; provided that R ¹ and A fluorinated alkyl 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.
R ¹ and R ² may further have other atoms other than the carbon atom, the hydrogen atom, and the fluorine atom.

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

Etc.

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

(Ii) Branched minimum structural unit:

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

Etc.

Among them, examples of the fluorinated alkyl group for Rf ² and R ⁶ include 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 - are preferred, high flame retardancy, rate characteristic and oxidation-resistant viewpoint of _{_{satisfactory, CF 3 CH 2 -, CF}} 3 CF ₂ CH ₂ — and HCF ₂ CF ₂ CH ₂ — are more preferred.

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 in terms of low viscosity.

Examples of the alkyl group not containing a 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 preferred 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, more preferably 60% by mass or less, and still more preferably 50% by mass or less.
In the present invention, the fluorine content is based on the structural formula of the fluorinated chain carbonate,
{(Number of fluorine atoms × 19) / molecular weight of fluorinated chain carbonate} × 100 (%)
The value calculated by

The fluorinated chain carbonate is preferably one of the following compounds from the viewpoint of low viscosity.

The content of the fluorinated chain carbonate is preferably 1 to 90% by volume in the solvent. When the content is within the above range, compatibility can be maintained.
The content of the fluorinated chain carbonate is more preferably 30% by volume or more in the solvent, more preferably 40% by volume or more, and more preferably 85% by volume or less in that the solubility of the salt can be maintained. 80 volume% or less is still more 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), CH ₃ CH ₂ OCOOCH ₃ (ethyl methyl carbonate: EMC). ), CH ₃ OCOOCH ₂ CH ₂ CH ₃ (methylpropyl carbonate), methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, and other hydrocarbon-based chain carbonates. Among these, at least one selected from the group consisting of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate is preferable.

The content of the non-fluorinated chain carbonate is preferably 0 to 99% by volume in the solvent, more preferably 1% by volume or more, and more preferably 90% by volume or less.

The solvent preferably contains the fluorinated saturated cyclic carbonate because a higher residual capacity retention rate can be obtained. In this case, the content of the fluorinated saturated cyclic carbonate is preferably 1 to 50% by volume, more preferably 3 to 40% by volume with respect to the solvent.

The solvent preferably contains the chain carbonate and the fluorinated saturated cyclic carbonate because a higher residual capacity retention rate is obtained. In this case, the volume ratio of the chain carbonate to the fluorinated saturated cyclic carbonate is preferably (99 to 50) / (1 to 50), more preferably (97 to 60) / (3 to 40).

The solvent is represented by the general formula (2):

(Wherein Rf ²¹ is —F, —CHF ₂ or —CF ₃ , R ²¹ , R ²⁴ and R ²⁵ are the same or different, and —H, —F, —CH ₃ , —CHF ₂ or —CF ₃ , R ^22, and R ²³ are the same or different, and —H, —F, —CH ₃ , —CHF _2, or —CF ₃ , or any one of R ²³ and the carbon atom to which R ²² is bonded to R ²³ It is preferable to include a fluorinated carbonate (2) represented by a single bond that forms a ring by bonding to bonded carbon atoms. Even when the electrolytic solution containing the fluorinated carbonate (2) is stored at a high temperature and used at a high voltage, an electrochemical device or module such as a lithium ion secondary battery having a high remaining capacity retention rate is obtained. Can do.

As fluorinated carbonate (2), general formula (3):
Rf ³¹ -CR ³¹ R ³² -OCOO-CR ³³ R ³⁴ R ³⁵
(Wherein Rf ³¹ is —F, —CHF ₂ or —CF ₃ , and R ³¹ to R ³⁵ are the same or different, —H, —F, —CH ₃ , —CHF ₂ or —CF ₃ ) Fluorinated chain carbonate (3) and general formula (4) shown:

(Wherein Rf ⁴¹ is —F, —CHF ₂ or —CF ₃ , and R ⁴¹ is —H, —F, —CH ₃ , —CHF ₂ or —CF ₃ ) 4)
More preferred is at least one selected from the group consisting of

R ³¹ to R ³⁵ are the same or different and are preferably —H or —CH ₃ , more preferably —H.

R ⁴¹ is preferably —H or —CH ₃ , more preferably —H.

As the fluorinated carbonate (2), any of the following compounds is particularly preferred.

As the content of the fluorinated carbonate (2), even when it is stored at a high temperature and used at a high voltage, an even higher residual capacity retention rate can be obtained. Is preferably 100 to 100% by volume, and more preferably 10 to 100% by volume.

The solvent preferably contains a fluorinated saturated cyclic carbonate (4) because even higher storage capacity retention can be obtained even when stored at a high temperature and used at a high voltage. In this case, the content of the fluorinated saturated cyclic carbonate (4) is preferably 5 to 30% by volume, more preferably 10 to 30% by volume with respect to the solvent.

As the above-mentioned solvent, even when it is stored at a high temperature and used at a high voltage, a higher residual capacity retention rate can be obtained, so that the fluorinated chain carbonate (3) and the fluorinated saturated cyclic carbonate (4) Or it is preferable that the said non-fluorinated chain carbonate and fluorinated saturated cyclic carbonate (4) are included.

The non-fluorinated chain carbonate is preferably at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

The volume ratio of the fluorinated chain carbonate (3) to the fluorinated saturated cyclic carbonate (4) is preferably (99 to 70) / (1 to 30), and (95 to 70) / (5 to 30). More preferred.

The volume ratio of the non-fluorinated chain carbonate to the fluorinated saturated cyclic carbonate (4) is preferably (99 to 70) / (1 to 30), more preferably (95 to 70) / (5 to 30). preferable.

The electrolytic solution of the present invention preferably contains an electrolyte salt.
Examples of the electrolyte salt include alkali metal salts, alkaline earth metal salts, metal salts using aluminum as a cation, ammonium salts, liquid salts (ionic liquids), inorganic polymer salts, organic polymer salts Any salt that can be used in the electrolyte solution, such as a salt of the above, can be used.

As an electrolyte salt of the electrolytic solution for a lithium ion secondary battery, an alkali metal salt is preferable, and a lithium salt is more preferable.

Arbitrary things can be used as said lithium salt, Specifically, the following are mentioned. For _{_{_{example, LiPF 6, LiBF 4, LiClO}}} 4, LiAlF 4, LiSbF 6, inorganic lithium salts LiTaF 6, LiWF ₇ and the like;
Lithium tungstates 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 Carboxylic acid lithium 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 Sulfonic acid lithium salts such as CF ₂ CF ₂ SO ₃ Li;
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-perfluoropropane disulfonylimide, LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) ;
Lithium metide salts such as LiC (FSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ ;
Lithium oxalatoborate salts such as lithium difluorooxalatoborate and lithium bis (oxalato) borate;
Lithium oxalate phosphate salts such as lithium tetrafluorooxalatophosphate, lithium difluorobis (oxalato) phosphate, lithium tris (oxalato) phosphate;
In addition, a salt represented by the formula: LiPF _a (C _n F _{2n + 1} ) _6-a (wherein 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 organic materials 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; and the like.

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-perfluoropropane disulfonylimide, LiC (FSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , lithium bis (oxalato) borate, lithium difluorooxalatoborate, lithium tetrafluorooxalatophosphate, 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 or the like is output characteristics and high-rate discharge characteristics, high-temperature storage characteristics, particularly preferred from the viewpoint that an effect of improving the cycle characteristics and the like.

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

In this case, there is no limit to the amount of LiBF ₄ or FSO ₃ Li based on 100% by mass of the entire electrolyte, and it is optional as long as the effects of the present invention are not significantly impaired. 0.01 mass% or more, preferably 0.1 mass% or more, and usually 30 mass% or less, preferably 20 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 the effect of suppressing deterioration due to high-temperature storage. As the organic lithium salt, 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-perfluoropropane disulfonylimide, LiC (FSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluorooxalate phosphate, lithium difluorobisoxalatophosphate, LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiPF ₃ (CF ₃ ) ₃ LiPF ₃ (C ₂ F ₅ ) ₃ or the like is preferable. In this case, the ratio of the organic lithium salt to 100% by mass of the entire electrolyte is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, and preferably 30% by mass or less, particularly Preferably it is 20 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, and more preferably 0. 0, from the viewpoint of ensuring the electric conductivity of the electrolytic solution in a good range and ensuring good performance of the electrochemical device. It is 4 mol / L or more, 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. On the other hand, if the concentration is too high, the electrical conductivity may decrease due to an increase in viscosity. Performance may be degraded.

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):

(Wherein R ^1a , R ^2a , R ^3a and R ^4a are the same or different, and all are alkyl groups optionally containing an ether bond having 1 to 6 carbon atoms; X ⁻ is an anion) Preferred examples include quaternary ammonium salts. In addition, the ammonium salt in which part or all of the hydrogen atoms are substituted with a fluorine atom and / or a fluorinated alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of improving oxidation resistance.

Specific examples include the general formula (IIa-1):

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

(Wherein 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 alkyl ether group containing trialkylammonium salt represented by the anion),
Etc. By introducing an alkyl ether group, the viscosity can be lowered.

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

Of these, BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ and SbF ₆ ⁻ are preferred from the viewpoint of good oxidation resistance and ion dissociation properties.

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, etc. I can get lost.

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

^{(Wherein, R 8a} and ^{R 9a} are the same or different and each is an alkyl group having 1 to 4 carbon atoms; X ^- is an anion; n2 is an integer of 0 to 5; n1 is an integer of 0 to 5) represented by Spirocyclic bipyrrolidinium salt, general formula (IIb-2):

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

^{(Wherein, R 12a} and ^{R 13a} are the same or different and each is an alkyl group having 1 to 4 carbon atoms; X ^- is an anion; n6 is an integer of 0 to 5; n5 is an integer of 0 to 5) represented by Spiro ring bipyrrolidinium salts are preferred. In addition, the spiro-ring bipyrrolidinium salt in which part or all of the hydrogen atoms are substituted with a fluorine atom and / or a fluorinated alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of improving oxidation resistance.

Anion X ^- of the preferred embodiment are the same as for (IIa). Among them, BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ or (C ₂ F ₅ SO ₂ ) ₂ N ⁻ is used because of its high dissociation property and low internal resistance under high voltage. preferable.

Preferable specific examples of the spiro ring bipyrrolidinium salt include, for example,

Etc.

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

(IIc) Imidazolium salt general formula (IIc):

(Wherein R ^14a and R ^15a are the same or different, and both are alkyl groups having 1 to 6 carbon atoms; X 2 ⁻ is an anion)
The imidazolium salt shown by can be illustrated preferably. In addition, the imidazolium salt in which part or all of the hydrogen atoms are substituted with a fluorine atom and / or a fluorinated alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of improving oxidation resistance.

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

As a preferable specific example, for example,

Etc.

This imidazolium salt is excellent in terms of low viscosity and good solubility.

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

(Wherein R ^16a is an alkyl group having 1 to 6 carbon atoms; X ⁻ is an anion)
N-alkylpyridinium salts represented by the formula are preferred. In addition, the N-alkylpyridinium salt in which part or all of the hydrogen atoms are substituted with a fluorine atom and / or a fluorinated alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of improving oxidation resistance.

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

As a preferable specific example, for example,

Etc.

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

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

(Wherein R ^17a and R ^18a are the same or different, and both are alkyl groups having 1 to 6 carbon atoms; X 2 ⁻ is an anion)
An N, N-dialkylpyrrolidinium salt represented by the formula is preferably exemplified. Further, the oxidation resistance of the N, N-dialkylpyrrolidinium salt in which some or all of the hydrogen atoms are substituted with fluorine atoms and / or fluorinated alkyl groups having 1 to 4 carbon atoms is improved. It is preferable from the point.

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

As a preferable specific example, for example,

Etc.

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,

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

Moreover, you may use lithium salt as electrolyte salt for electrical double layer capacitors. Examples of the lithium _{_{_{salt, LiPF 6, LiBF 4, LiAsF}}} 6, LiSbF 6, LiN (SO 2 C 2 H 5) 2 is preferred.
In order to further improve the capacity, a magnesium salt may be used. 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 ammonium salt, the concentration is preferably 1.1 mol / liter or more. If it is less than 1.1 mol / liter, not only the low-temperature characteristics are deteriorated, but also the initial internal resistance is increased. The concentration of the electrolyte salt is more preferably 1.25 mol / liter or more.
The concentration is preferably 1.7 mol / liter or less, more preferably 1.5 mol / liter or less, from the viewpoint of low temperature characteristics.
When the ammonium salt is triethylmethylammonium tetrafluoroborate (TEMABF ₄ ), the concentration is preferably 1.1 to 1.4 mol / liter from the viewpoint of excellent low-temperature characteristics.
In the case of spirobipyrrolidinium tetrafluoroborate (SBPBF ₄ ), the amount is preferably 1.3 to 1.7 mol / liter.

The electrolytic solution of the present invention preferably further contains polyethylene oxide having a weight average molecular weight of 2000 to 4000 and having —OH, —OCOOH, or —COOH at the terminal.
By containing such a compound, the stability of the electrode interface is 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.
Of these, 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 become better.

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

The polyethylene oxide content is preferably 1 × 10 ⁻⁶ to 1 × 10 ⁻² mol / kg in the electrolytic solution. When there is too much content of the said polyethylene oxide, there exists a possibility of impairing the characteristic of an electrochemical device.
The polyethylene oxide content is more preferably 5 × 10 ⁻⁶ mol / kg or more.

The electrolytic solution of the present invention may further contain at least one selected from the group consisting of unsaturated cyclic carbonates and cyclic sulfonic acid compounds. By containing these compounds, it is possible to suppress deterioration of the characteristics of the electrochemical device.

The unsaturated cyclic carbonate is a cyclic carbonate containing an unsaturated bond, that is, a cyclic carbonate having at least one carbon-carbon unsaturated bond in the molecule.

Examples of unsaturated cyclic carbonates include vinylene carbonates, aromatic carbonates, ethylene carbonates substituted with a substituent having a carbon-carbon double bond or carbon-carbon triple bond, phenyl carbonates, vinyl carbonates, allyl carbonates, Catechol carbonates etc. are mentioned.

The vinylene carbonates include vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl vinylene carbonate, 4,5-divinyl vinylene carbonate, allyl vinylene carbonate, 4 , 5-diallyl vinylene carbonate, 4-fluoro vinylene carbonate, 4-fluoro-5-methyl vinylene carbonate, 4-fluoro-5-phenyl vinylene carbonate, 4-fluoro-5-vinyl vinylene carbonate, 4-allyl-5-fluoro Examples include vinylene carbonate.

Specific examples of ethylene carbonates substituted with an aromatic ring or a substituent having a carbon-carbon double bond or carbon-carbon triple bond include vinyl ethylene carbonate, 4,5-divinylethylene carbonate, 4-methyl-5- Vinyl ethylene carbonate, 4-allyl-5-vinyl ethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, 4-vinyl-5-ethynyl ethylene 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 diallyl carbonate, 4-methyl-5-allyl carbonate and the like.

Among these, as unsaturated cyclic carbonates, vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, vinyl vinylene carbonate, 4,5-vinyl vinylene carbonate, allyl vinylene carbonate, 4,5-diallyl vinylene carbonate, 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 Ethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, 4-vinyl-5-ethynyl ether Ren carbonate is preferred. Vinylene carbonate, vinyl ethylene carbonate, and ethynyl ethylene carbonate are particularly preferable because they form a more stable interface 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. If it is this range, it will be easy to ensure the solubility of the unsaturated cyclic carbonate with respect to electrolyte solution, and the effect of this invention will fully be expressed easily. The molecular weight of the unsaturated cyclic carbonate is more preferably 80 or more, and more preferably 150 or less.

The production method of the unsaturated cyclic carbonate is not particularly limited, and can be produced by arbitrarily selecting a known method.

An unsaturated cyclic carbonate may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a 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 still more 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 still more preferably 3% by mass or less. If it is within the above range, the electrochemical device using the electrolytic solution is likely to exhibit a sufficient cycle characteristic improving effect, the high-temperature storage characteristic is lowered, the amount of gas generation is increased, and the discharge capacity maintenance rate is lowered It is easy to avoid such a situation.

In addition to the non-fluorinated unsaturated cyclic carbonate as described above, a fluorinated unsaturated cyclic carbonate can also be suitably used as the unsaturated cyclic carbonate.
The fluorinated unsaturated cyclic carbonate is a cyclic carbonate having an unsaturated bond and a fluorine atom.
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 most preferably 1 or 2 fluorine atoms.

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.
Fluorinated vinylene carbonate derivatives include 4-fluoro vinylene carbonate, 4-fluoro-5-methyl vinylene carbonate, 4-fluoro-5-phenyl vinylene carbonate, 4-allyl-5-fluoro vinylene carbonate, 4-fluoro-5- And vinyl vinylene carbonate.

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, 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-diflu B-4,5-diallylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4,4-difluoro-5-phenylethylene carbonate, 4,5-difluoro-4- Examples thereof include phenylethylene carbonate.

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, -Fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, 4,5-difluoro-4,5-diallylethylene carbonate form a stable interface protective film, More 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. If it is this range, it will be easy to ensure the solubility of the fluorinated unsaturated cyclic carbonate with respect to electrolyte solution, and the effect of this invention will be easy to be expressed.

The production method of the fluorinated unsaturated cyclic carbonate is not particularly limited, and can be produced by arbitrarily selecting a known method.

The molecular weight is more preferably 100 or more, and more preferably 200 or less.

The said fluorinated unsaturated cyclic carbonate may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

Further, 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 in 100% by mass of the electrolytic solution, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and further preferably 0.2% by mass or more. Moreover, it is preferably 5% by mass or less, more preferably 4% by mass or less, and still more preferably 3% by mass or less. Within this range, the electrochemical device using the electrolytic solution is likely to exhibit a sufficient cycle characteristic improvement effect, and the high-temperature storage characteristic is reduced, the amount of gas generated is increased, and the discharge capacity maintenance rate is reduced. It is easy to avoid such a situation.

Examples of the cyclic sulfonic acid compound include 1,3-propane sultone, 1,4-butane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, and 3-fluoro-1 , 3-propane sultone and the like. Among these, the electrolyte solution of the present invention preferably contains 1,3-propane sultone and / or 1,4-butane sultone in that the high temperature characteristics can be improved.
The content of the cyclic sulfonic acid compound is preferably 0.1 to 10% by mass in the electrolytic solution, more preferably 1% by mass or more, and more preferably 5% by mass or less.

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

As the overcharge inhibitor, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, Partially fluorinated products 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 And a fluorine-containing anisole compound. Of these, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, terphenyl partially hydrogenated, 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, biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, Using at least one selected from aromatic compounds not containing oxygen, such as t-amylbenzene, and at least one selected from oxygen-containing aromatic compounds such as diphenyl ether, dibenzofuran, etc. is an overcharge prevention property and a high temperature storage property. From the standpoint of balance.

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 anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, anhydrous Carboxylic anhydrides such as itaconic acid, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride and phenylsuccinic anhydride; 2,4,8,10-tetraoxaspiro [5.5 ] Spiro compounds such as undecane, 3,9-divinyl-2,4,8,10-tetraoxaspiro [5.5] undecane; ethylene sulfite, 1,3-propane sultone, 1-fluoro-1,3- Propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro Oro-1,3-propane sultone, 1-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 2-fluoro-1-propene-1,3-sultone, 3-fluoro -1-propene-1,3-sultone, 1,4-butane sultone, 1-butene-1,4-sultone, 3-butene-1,4-sultone, methyl fluorosulfonate, ethyl fluorosulfonate, methanesulfonic acid Methyl, ethyl methanesulfonate, busulfan, sulfolene, diphenylsulfone, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide, methyl vinylsulfonate, ethyl vinylsulfonate, allyl vinylsulfonate, vinylsulfonic acid Propargyl, methyl allyl sulfonate, ethyl allyl sulfonate, allyl Sulfur-containing compounds such as allyl sulfonate, propargyl allylsulfonate, 1,2-bis (vinylsulfonoxy) ethane; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone Nitrogen-containing compounds such as 1,3-dimethyl-2-imidazolidinone and N-methylsuccinimide; trimethyl phosphite, triethyl phosphite, triphenyl phosphite, trimethyl phosphate, triethyl phosphate, triphosphate Phosphorus-containing compounds such as phenyl, dimethyl methylphosphonate, diethyl ethylphosphonate, dimethyl vinylphosphonate, diethyl vinylphosphonate, ethyl diethylphosphonoacetate, methyl dimethylphosphinate, ethyl diethylphosphinate, trimethylphosphine oxide, triethylphosphine oxide; Hep Examples 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, capacity maintenance characteristics and cycle characteristics after high temperature storage can be improved.

The blending amount of 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 can be sufficiently exhibited, and it is easy to avoid a situation in which battery characteristics such as high-load discharge characteristics deteriorate. The blending amount of other auxiliaries is more preferably 0.1% by mass or more, further preferably 0.2% by mass or more, more preferably 3% by mass or less, still more preferably 1% by mass or less. .

The electrolyte solution of the present invention includes cyclic and chain carboxylic acid esters, ether compounds, nitrogen-containing compounds, boron-containing compounds, organosilicon-containing compounds, non-flammable (flame retardant) agents, and interfaces as long as the effects of the present invention are not impaired. Other solvents or additives such as activators, high dielectric additives, cycle characteristics and rate characteristics improvers may also be included.

Examples of the cyclic carboxylic acid ester include those having 3 to 12 total carbon atoms in the structural formula. Specific examples include gamma butyrolactone, gamma valerolactone, gamma caprolactone, epsilon caprolactone, and the like. Among these, gamma butyrolactone is particularly preferable from the viewpoint of improving the characteristics of the electrochemical device derived from the improvement of the degree of lithium ion dissociation.

The compounding quantity of cyclic carboxylic acid ester is 100 mass% of solvent normally, Preferably it is 0.1 mass% or more, More preferably, it is 1 mass% or more. Within this range, the electrical conductivity of the electrolytic solution is improved, and the large current discharge characteristics of the electrochemical device are easily improved. Moreover, the compounding quantity of cyclic carboxylic acid ester becomes like this. Preferably it is 10 mass% or less, More preferably, it is 5 mass% or less. By setting the upper limit in this way, the viscosity of the electrolytic solution is set in 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 in a favorable range. Make it easier.

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

(Wherein X ¹⁵ to X ²⁰ are the same or different and all are —H, —F, —Cl, —CH ₃ or a fluorinated alkyl group; provided that at least one of X ¹⁵ to X ²⁰ is a fluorinated alkyl A fluorine-containing lactone represented by the following formula:

Examples of the fluorinated alkyl group for 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 an effect of improving safety.

If at least one of X ¹⁵ to X ²⁰ is a fluorinated alkyl group, —H, —F, —Cl, —CH ₃ or the fluorinated alkyl group is substituted at only one position of X ¹⁵ to X ^20. Alternatively, a plurality of locations may be substituted. Preferably, it is 1 to 3 sites, more preferably 1 to 2 sites, from the viewpoint of good solubility of the electrolyte salt.

The substitution position of the fluorinated alkyl group is not particularly limited. However, since the synthesis yield is good, X ¹⁷ and / or X ¹⁸ is particularly preferably X ¹⁷ or X ¹⁸ is a fluorinated alkyl group, particularly —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.

Examples of the fluorine-containing lactone include those represented by the following formula (F):

(In the formula, one of A and B is CX ²⁶ X ²⁷ (X ²⁶ and X ²⁷ are the same or different, and each of them is —H, —F, —Cl, —CF ₃ , —CH ₃ or a hydrogen atom) An alkylene group which may be substituted with a halogen atom and may contain a hetero atom in the chain), the other is an oxygen atom; Rf ¹² is a fluorinated alkyl group or a fluorinated group which may have an ether bond X ²¹ and X ²² are the same or different; all are —H, —F, —Cl, —CF ₃ or CH ₃ ; X ²³ to X ²⁵ are the same or different, and both are —H, —F , -Cl or an alkyl group in which a hydrogen atom may be substituted with a halogen atom and may contain a hetero atom in the chain; a fluorine-containing lactone represented by n = 0 or 1).

Examples of the fluorine-containing lactone represented by the formula (F) include the following formula (G):

(In the formula, A, B, Rf ¹² , X ²¹ , X ²² and X ²³ are the same as those in formula (F)), the 5-membered ring structure is easy to synthesize and has chemical stability. It is preferably mentioned from a favorable point, and further, by the combination of A and B, the following formula (H):

(Wherein Rf ¹² , X ²¹ , X ²² , X ²³ , X ²⁶ and X ²⁷ are the same as those in formula (F)), and the following formula (I):

(Wherein Rf ¹² , X ²¹ , X ²² , X ²³ , X ²⁶ and X ²⁷ are the same as those in formula (F)).

Among these, the point that the excellent characteristics such as high dielectric constant and high withstand voltage can be exhibited especially, and the characteristics as the 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

Etc.
By including the fluorinated cyclic carboxylic acid ester, effects such as improvement in ionic conductivity, improvement in safety, and improvement in stability at high temperatures can be obtained.

Examples of the chain carboxylic acid ester include those having 3 to 7 carbon atoms in the structural formula. Specifically, methyl acetate, ethyl acetate, acetate n-propyl, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, Isopropyl propionate, n-butyl propionate, isobutyl propionate, t-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methyl isobutyrate, ethyl isobutyrate, isobutyric acid-n- Examples include propyl and isopropyl isobutyrate.

Among them, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, etc. are ions due to viscosity reduction. It is preferable from the viewpoint of improvement of conductivity.

Moreover, fluorinated chain carboxylic acid ester can also be used suitably. As the fluorine-containing ester, the following formula (J):
Rf ¹⁰ COORf ¹¹ (J)
(Wherein Rf ¹⁰ is a fluorinated alkyl group having 1 to 2 carbon atoms, Rf ¹¹ is a fluorinated alkyl group having 1 to 4 carbon atoms), and the flame retardant property is high, And it is preferable from the viewpoint of good compatibility with other solvents and oxidation resistance.

Examples of Rf ¹⁰ include CF _3- , CF ₃ CF _2- , HCF ₂ CF _2- , HCF _2- , CH ₃ CF _2- , CF ₃ CH _2- and the like, among which CF _3- , CF ₃ CF ₂ -is particularly preferable from the viewpoint of good rate characteristics.

Examples of Rf ¹¹ include 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., among others, CF ₃ CH _2- , (CF ₃ ) ₂ CH—, C ₂ F ₅ CH ₂ —, and CF ₂ HCF ₂ CH ₂ — are particularly preferred from the viewpoint of good compatibility with other solvents.

Specific examples of the fluorinated chain carboxylic acid ester include, for example, CF ₃ C (═O) OCH ₂ CF ₃ , CF ₃ C (═O) OCH ₂ CH ₂ CF ₃ , and CF ₃ C (═O) OCH ₂ C. _{One or more of 2} F ₅ , CF ₃ C (═O) OCH ₂ CF ₂ CF ₂ H, CF ₃ C (═O) OCH (CF ₃ ) _2, etc. can be exemplified, among which 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 However, the compatibility with other solvents and the rate characteristics are particularly preferable.

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.
Examples of the chain ether 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 include ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether and the like.

Further, as the ether compound, a fluorinated ether can also be suitably used.
As the fluorinated ether, the following general formula (K):
Rf ¹ -O-Rf ² (K)
(In the formula, Rf ¹ and Rf ² 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, provided that at least one of Rf ¹ and Rf ² is fluorine. A fluorinated ether (K) represented by the following formula: By containing the fluorinated ether (K), the flame retardancy of the electrolytic solution is improved, and the stability and safety at high temperature and high voltage are improved.

In the general formula (K), at least one of Rf ¹ and Rf ² may be a fluorinated alkyl group having 1 to 10 carbon atoms. However, the flame retardancy of the electrolyte solution, stability at high temperature and high voltage, safety From the viewpoint of further improving the properties, both Rf ¹ and Rf ² are preferably fluorinated alkyl groups having 1 to 10 carbon atoms. In this case, Rf ¹ and Rf ² may be the same or different from each other.
In particular, Rf ¹ and Rf ² are the same or different, Rf ¹ is a fluorinated alkyl group having 3 to 6 carbon atoms, and Rf ² is a fluorinated alkyl group having 2 to 6 carbon atoms. More preferred.

When the total carbon number of Rf ¹ and Rf ² is too small, the boiling point of the fluorinated ether becomes too low, and when the carbon number of Rf ¹ or Rf ² is too large, the solubility of the electrolyte salt decreases, and other solvents As a result, the compatibility with the resin begins to have an adverse effect, and since the viscosity increases, the rate characteristics are reduced. When Rf ¹ has 3 or 4 carbon atoms and Rf ² has 2 or 3 carbon atoms, it is advantageous in that it has excellent boiling point and rate characteristics.

The fluorinated ether (K) preferably has a fluorine content of 40 to 75% by mass. When it has a fluorine content in this range, it is particularly excellent in the balance between incombustibility and compatibility. Moreover, it is preferable also from a point with favorable oxidation resistance and safety | security.
The lower limit of the fluorine content is more preferably 45% by mass, still more preferably 50% by mass, and particularly preferably 55% by mass. The upper limit is more preferably 70% by mass, and still more preferably 66% by mass.
The fluorine content of the fluorinated ether (K) is {(number of fluorine atoms × 19) / molecular weight of the fluorinated ether (K)} × 100 (% based on the structural formula of the fluorinated ether (K). ).

Examples of Rf ¹ include 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.
Rf ² may be, for example, CF ₃ CF ₂ CH ₂ —, CF ₃ CFHCF ₂ —, CF ₂ HCF ₂ CF ₂ —, CF ₂ HCF ₂ CH ₂ —, CF ₃ CF ₂ CH ₂ CH ₂ —, CF ₃ CFHCF ₂ CH ₂ —, CF ₂ HCF ₂ CF ₂ CF ₂ —, CF ₂ HCF ₂ CF ₂ CH ₂ —, CF ₂ HCF ₂ CH ₂ CH ₂ —, CF ₂ HCF (CF ₃ ) CH ₂ —, CF ₂ HCF ₂ —, CF ₂ HCH ₂ —, CH ₃ CF ₂ — and the like can be mentioned.

Specific examples of the fluorinated ether (K) 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} or the like can be mentioned.

Among them, one containing HCF ₂ — or CF ₃ CFH— at one or both ends is excellent in polarizability and can give a fluorinated ether (K) having a high boiling point. The boiling point of the fluorinated ether (K) is preferably 67 to 120 ° C. More preferably, it is 80 degreeC or more, More preferably, it is 90 degreeC or more.

Examples of such a fluorinated ether (K) 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 , and 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 1 type of H, etc. or two The above is mentioned.
Of these, HCF ₂ CF ₂ CH ₂ OCF ₂ CFHCF ₃ (boiling point 106 ° C.), CF ₃ CF ₂ CH is advantageous because of its high boiling point, compatibility with other solvents, and good solubility of the electrolyte salt. 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.). And at least one 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.). One type is more preferable.

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 fluorinated compounds thereof. Is mentioned. Among them, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether have high solvating ability to lithium ions and improve the degree of ion dissociation. Dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferable because they have low viscosity and give high ionic conductivity.

Examples of the nitrogen-containing compound include nitrile, fluorine-containing nitrile, carboxylic acid amide, fluorine-containing carboxylic acid amide, sulfonic acid amide, and fluorine-containing sulfonic acid amide. Further, 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxaziridinone, 1,3-dimethyl-2-imidazolidinone, N-methylsuccinimide and the like can be used.

Examples of the boron-containing compound include boric acid esters such as trimethyl borate and triethyl borate, boric 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 incombustible (flame retardant) agent include phosphate esters and phosphazene compounds. Examples of the phosphate ester include fluorine-containing alkyl phosphate esters, non-fluorinated alkyl phosphate esters, and aryl phosphate esters. Especially, it is preferable that it is a fluorine-containing alkyl phosphate ester at the point which can exhibit a nonflammable effect in a small quantity.

Specific examples of the fluorine-containing alkyl phosphate ester include fluorine-containing dialkyl phosphate esters described in JP-A No. 11-233141 and cyclic alkyl phosphate esters described in JP-A No. 11-283669. Or fluorine-containing trialkyl phosphate ester etc. are mentioned.

As the non-flammable (flame retardant) agent, (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. From the viewpoint of good cycle characteristics and rate characteristics, a fluorine atom It is preferable that it contains.

As such a surfactant containing a fluorine atom, for example, the following formula:
Rf ¹ COO ⁻ M ⁺
(Wherein Rf ¹ is a fluorinated alkyl group that may contain an ether bond having 3 to 10 carbon atoms; M ⁺ is Li ⁺ , Na ⁺ , K ⁺ or NHR ′ ₃ ⁺ (R ′ is the same or different) , Each of which is H or an alkyl group having 1 to 3 carbon atoms), or a fluorine-containing carboxylate represented by the following formula:
Rf ² SO ₃ ^- M ⁺
(Wherein Rf ² is a fluorinated alkyl group optionally containing an ether bond having 3 to 10 carbon atoms; M ⁺ is Li ⁺ , Na ⁺ , K ⁺ or NHR ′ ₃ ⁺ (R ′ is the same or different) These are preferably fluorine-containing sulfonates represented by the following formula: H or an alkyl group having 1 to 3 carbon atoms.

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 reducing the charge / discharge cycle characteristics.

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

Examples of the cycle characteristic and rate characteristic 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 (plasticized) gel electrolytic solution.

Examples of such a polymer material include conventionally known polyethylene oxide and polypropylene oxide, modified products thereof (JP-A-8-222270 and JP-A-2002-1000040); polyacrylate polymers, polyacrylonitrile, and polyvinylidene fluoride. Fluorine resins such as vinylidene fluoride-hexafluoropropylene copolymer (JP-A-4-506726, JP-A-8-507407, JP-A-10-294131); Examples include composites with resins (Japanese Patent Laid-Open Nos. 11-35765 and 11-86630). In particular, it is desirable to use polyvinylidene fluoride or a vinylidene fluoride-hexafluoropropylene copolymer as the polymer material for the gel electrolyte.

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

This ion conductive compound has the formula (1-1):
A- (D) -B (1-1)
[Wherein D represents the formula (2-1):
-(D1) _n- (FAE) _m- (AE) _p- (Y) _q- (2-1)
(In the formula, D1 represents the formula (2a):

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

(Wherein, Rfa is hydrogen atom, a crosslinkable functional group which may have a fluorinated alkyl group; R ¹¹ is a group or a bond that binds the Rfa main chain) fluorinated alkyl group in the side chain represented by Ether units having:
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. An aromatic hydrocarbon group which may be present; R ¹² is an ether unit represented by R ¹³ and a group or a bond which bonds the main chain;
Y represents the formulas (2d-1) to (2d-3):

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

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

The electrolytic solution of the present invention preferably contains 0.5 to 70 ppm of HF. By containing HF, the film formation of the additive can be promoted. When the content of HF is too small, the film forming ability of the additive on the negative electrode is lowered, and the characteristics of the electrochemical device tend to be lowered. Moreover, when there is too much HF content, there exists a tendency for the oxidation resistance of electrolyte solution to fall under the influence of HF. Even if the electrolytic solution of the present invention contains HF in the above range, the high temperature storage stability recovery capacity ratio of the electrochemical device does not decrease.
The content of HF is more preferably 1 ppm or more, and further preferably 2.5 ppm or more. The content of HF is more preferably 60 ppm or less, still more preferably 50 ppm or less, and particularly preferably 30 ppm or less.
The content of HF can be measured by a neutralization titration method.

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

The electrolyte solution of the present invention can be suitably applied to electrochemical devices such as lithium ion secondary batteries and electric double layer capacitors. Such an electrochemical device including the electrolytic solution of the present invention is also one aspect of the present invention.

Electrochemical devices include lithium ion secondary batteries, capacitors (electric double layer capacitors), radical batteries, solar cells (especially dye-sensitized solar cells), fuel cells, various electrochemical sensors, electrochromic devices, and electrochemical switching. Examples thereof include an element, an aluminum electrolytic capacitor, a tantalum electrolytic capacitor, and a lithium ion secondary battery and an electric double layer capacitor are preferable.
A module including the electrochemical device is also one aspect of the present invention.

The present invention is also a lithium ion secondary battery including the electrolytic solution of the present invention.

The lithium ion secondary battery may include a positive electrode, a negative electrode, and the above-described 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. For example, a material containing lithium and at least one transition metal is preferable. Specific examples include lithium-containing transition metal composite oxides and lithium-containing transition metal phosphate compounds. Especially, as a positive electrode active material, the lithium containing transition metal complex oxide which produces a high voltage is especially preferable.
Examples of the lithium-containing transition metal composite oxide include:
Formula: Li _a Mn _2-b M ¹ _b O ₄ (where 0.9 ≦ a; 0 ≦ b ≦ 1.5; M ¹ is Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, A lithium-manganese spinel composite oxide represented by V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge).
Formula: LiNi _1-c M ² _c O ₂ (where 0 ≦ c ≦ 0.5; M ² is Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, 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 (where 0 ≦ d ≦ 0.5; M ³ is Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, 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 can be provided because the lithium ion secondary battery with high energy density and high output can be provided. Or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is preferred.

As other positive electrode active materials, 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 , LiNi _{0 _{_{_{.5 Mn 1.5 O 4, LiV 3}}}} O 6 , and the like.

In addition, it is preferable to include lithium phosphate in the positive electrode active material because continuous charge characteristics are improved. Although there is no restriction | limiting in the use of lithium phosphate, It is preferable to mix and use the said positive electrode active material and lithium phosphate. The lower limit of the amount of lithium phosphate to be used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and further preferably 0.5% by mass with respect to the total of the positive electrode active material and lithium phosphate. %, 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.

Moreover, you may use what the substance of the composition different from this adhered to the surface of the said positive electrode active material. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate, and carbon.

For example, these surface adhering substances are dissolved or suspended in a solvent, impregnated and added to the positive electrode active material, and dried. After the surface adhering substance precursor is dissolved or suspended in a solvent and impregnated and added to the positive electrode active material, It can be made to adhere 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 simultaneously. In addition, when making carbon adhere, the method of making carbonaceous adhere mechanically later in the form of activated carbon etc. can also be used, for example.

The amount of the surface adhering substance is, in terms of mass with respect to the positive electrode active material, preferably 0.1 ppm or more, more preferably 1 ppm or more, further preferably 10 ppm or more, and the upper limit, preferably 20% or less, more preferably as the lower limit. Is used at 10% or less, more preferably 5% or less. The surface adhering substance can suppress the oxidation reaction of the electrolyte solution on the surface of the positive electrode active material and can improve the battery life. However, when the amount of the adhering quantity is too small, the effect is not sufficiently manifested. If it is too high, the resistance may increase in order to inhibit the entry and exit of lithium ions.

Examples of the shape of the particles of the positive electrode active material include a lump shape, a polyhedron shape, a sphere shape, an oval sphere shape, a plate shape, a needle shape, and a column shape as conventionally used. Moreover, primary particles may aggregate 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. If the tap density of the positive electrode active material is lower than the lower limit, the amount of the required dispersion medium increases when the positive electrode active material layer is formed, and the necessary amount of conductive material and binder increases, so that the positive electrode to the positive electrode active material layer The filling rate of the active material is restricted, and the battery capacity may be restricted. By using a complex oxide powder having a high tap density, a high-density positive electrode active material layer can be formed. In general, the tap density is preferably as large as possible, and there is no particular upper limit, but if it is too large, diffusion of lithium ions using the electrolytic solution in the positive electrode active material layer as a medium is rate-limiting, and load characteristics may be easily reduced. The upper limit is preferably 4.0 g / cm ³ or less, more preferably 3.7 g / cm ³ or less, and still more preferably 3.5 g / cm ³ or less.
In the present invention, the tap density is 5 to 10 g of the positive electrode active material powder in a 10 ml glass measuring cylinder and tapped 200 times with a stroke of about 20 mm (tap density) g / cm ^3. Asking.

The median diameter d50 of the positive electrode active material particles (secondary particle diameter when primary particles aggregate to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably. Is 0.8 μm or more, most preferably 1.0 μm or more, preferably 30 μm or less, more preferably 27 μm or less, further preferably 25 μm or less, and most preferably 22 μm or less. If the lower limit is not reached, a high tap density product may not be obtained. If the upper limit is exceeded, it takes time to diffuse lithium in the particles, so that the battery performance may be lowered, or the positive electrode of the battery, that is, the active material When a conductive material, a binder, or the like is slurried with a solvent and applied as a thin film, problems such as streaking may occur. Here, by mixing two or more kinds of the positive electrode active materials having different median diameters d50, it is possible to further improve the filling property at the time of forming the positive electrode.

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 a particle size distribution meter, a 0.1% by mass sodium hexametaphosphate aqueous solution is used as a dispersion medium for measurement, and a measurement refractive index of 1.24 is set after ultrasonic dispersion for 5 minutes. 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, and still more preferably 0.8. 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 the above upper limit is exceeded, it is difficult to form spherical secondary particles, which adversely affects the powder filling property, or the specific surface area is greatly reduced, so that there is a high possibility that battery performance such as output characteristics will deteriorate. is there. On the other hand, when the value falls below the lower limit, there is a case where problems such as inferior reversibility of charge / discharge are usually caused because crystals are not developed.

In the present invention, the primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at a magnification of 10000 times, 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 obtained by taking the average value. It is 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 / g or less, more preferably 40 m ² / g or less, and further preferably 30 m ² / g or less. If the BET specific surface area is smaller than this range, the battery performance tends to be lowered. If the BET specific surface area is larger, the tap density is difficult to increase, and a problem may occur in applicability when forming the positive electrode active material layer.

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

When the lithium ion secondary battery of the present invention is used as a large-sized lithium ion secondary battery for a hybrid vehicle or a distributed power source, high output is required. Therefore, the positive electrode active material particles are mainly secondary particles. It is preferable that
The particles of the positive electrode active material preferably contain 0.5 to 7.0% by volume of fine particles having an average secondary 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 further accelerated. Output performance can be improved.

As a manufacturing method of the positive electrode active material, a general method is used as a manufacturing method of the inorganic compound. In particular, various methods are conceivable for preparing a spherical or elliptical active material. For example, a transition metal source material is dissolved or pulverized and dispersed in a solvent such as water, and the pH is adjusted while stirring. And a spherical precursor is prepared and recovered, and dried as necessary. Then, a Li source such as LiOH, Li ₂ CO ₃ , LiNO ₃ is added, and the active material is obtained by baking at a high temperature. .

For the production of the positive electrode, the positive electrode active material may be used alone, or two or more of the different compositions may be used in any combination or ratio. A preferable combination in this case is a combination of LiCoO ₂ and LiMn ₂ O ₄ such as LiNi _0.33 Co _0.33 Mn _0.33 O ₂ or a part of this Mn substituted with another transition metal or the like. Or a combination with LiCoO ₂ or a part of this Co substituted with another transition metal or the like.

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 mixture, from the viewpoint 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. Moreover, an upper limit becomes like this. Preferably it is 99 mass% or less, More preferably, it is 98 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. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

The positive electrode mixture preferably further contains a binder, a thickener, and a conductive material.
As the above-mentioned binder, any material can be used as long as it is a material that is safe with respect to the solvent and the electrolyte used in the production of the electrode. For example, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene , SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, NBR (Acrylonitrile-butadiene rubber), fluoro rubber, ethylene-propylene rubber, styrene / butadiene / styrene block copolymer or its hydrogenated product, EPDM (ethylene / propylene / diene terpolymer), styrene / ethylene / Tadiene / ethylene copolymer, styrene / isoprene / styrene block copolymer or hydrogenated product thereof, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer Examples thereof include polymers, fluorinated polyvinylidene fluoride, tetrafluoroethylene / ethylene copolymers, and polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions). In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

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 a ratio of the binder in the positive electrode active material layer. Usually, it is 80 mass% or less, Preferably it is 60 mass% or less, More preferably, it is 40 mass% or less, Most preferably, it is 10 mass% or less. When the ratio of the binder is too low, the positive electrode active material cannot be sufficiently retained and the positive electrode has insufficient mechanical strength, which may deteriorate battery performance such as cycle characteristics. On the other hand, if it is too high, battery capacity and conductivity may be reduced.

Examples of the thickener include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. 1 type may be used independently or 2 or more types may be used together by arbitrary combinations and a 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 not more than mass%, more preferably not more than 2 mass%. Below this range, applicability may be significantly reduced. If it exceeds, the ratio of the active material in the positive electrode active material layer may decrease, and there may be a problem that the capacity of the battery decreases and a problem that the resistance between the positive electrode active materials increases.

A known conductive material can be arbitrarily used as the conductive material. Specific examples include metal materials such as copper and nickel, 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. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a 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. % Or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

As the solvent for forming the slurry, the positive electrode active material, the conductive material, the binder, and a solvent capable of dissolving or dispersing the thickener used as necessary may be used. There is no restriction, 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; ketones such as acetone, methyl ethyl ketone, and cyclohexanone. Esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N, N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide and tetrahydrofuran (THF); N-methylpyrrolidone (NMP) Amides such as dimethylformamide and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphalamide and dimethylsulfoxide.

Examples of the material for the positive electrode current collector 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. Among these, a metal material, particularly aluminum or an alloy thereof is 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, and foam metal in the case of a metal material. A thin film, a carbon cylinder, etc. are mentioned. Of these, metal thin films are preferred. In addition, you may form a thin film suitably in mesh shape. 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 for the current collector may be insufficient. Conversely, if the thin film is thicker than this range, the handleability may be impaired.

Moreover, it is also preferable from the viewpoint of reducing the electrical contact resistance between the current collector and the positive electrode active material layer that the surface of the current collector is coated with a conductive additive. Examples of the conductive assistant include noble metals such as carbon, 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 electrolyte injection) / (thickness of the current collector) is 20 Is 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. Above this range, the current collector may generate heat due to Joule heat during high current density charge / discharge. Below this range, the volume ratio of the current collector to the positive electrode active material increases and the battery capacity may decrease.

The positive electrode may be manufactured by a conventional method. For example, the above-mentioned positive electrode active material is added with the above-mentioned binder, thickener, conductive material, solvent, etc. to form a slurry-like positive electrode mixture, which is applied to a current collector, dried and then pressed. A method of densification is mentioned.

The densification can be performed 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, still more preferably 2.2 g / cm ³ or more, and preferably 5 g / cm ³ or less. More preferably, it is 4.5 g / cm < ³ > or less, More preferably, it is the range of 4 g / cm < ³ > or less. If it exceeds this range, the permeability of the electrolyte solution to the vicinity of the current collector / active material interface decreases, and the charge / discharge characteristics particularly at a high current density decrease, and a high output may not be obtained. On the other hand, if it is lower, the conductivity between the active materials is lowered, the battery resistance is increased, and a high output may not be obtained.

When using the electrolytic solution of the present invention, 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 increasing the stability at high output and high temperature. Specifically, the sum 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. The outer surface area of the battery outer case, in the case of a square shape with a bottom, is the total area calculated from the vertical, horizontal, and thickness dimensions of the case part filled with the power generation element excluding the protruding part of the terminal. 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 the structure in which the positive electrode mixture layer is formed on both sides via the current collector foil. , The sum of the areas where each surface is calculated separately.

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 composite layer obtained by subtracting the metal foil thickness of the core material is preferably as a 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.

Moreover, you may use what adhered the substance of the composition different from this to the surface of the said positive electrode plate. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate, and carbon.

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

Examples of the negative electrode active material include carbonaceous materials capable of occluding and releasing lithium, such as organic pyrolysis products and artificial graphite and natural graphite under various pyrolysis conditions; occlusion / release of lithium such as tin oxide and silicon oxide. Possible metal oxide materials; lithium metal; various lithium alloys; lithium-containing metal composite oxide materials. These negative electrode active materials may be used in combination of two or more.

As a carbonaceous material capable of occluding and releasing lithium, artificial graphite or purified natural graphite produced by high-temperature treatment of graphitizable pitch obtained from various raw materials, or surface treatment with pitch or other organic substances on these graphites And carbonized material obtained by carbonizing natural graphite, artificial graphite, artificial carbonaceous material, and artificial graphite material at least once in the range of 400 to 3200 ° C., and a negative electrode active material layer. A carbonaceous material comprising at least two kinds of carbonaceous materials having different crystallinity and / or having an interface in contact with the different crystalline carbonaceous materials, and at least two kinds of different orientations of the negative electrode active material layer A carbonaceous material having an interface with which the carbonaceous material is in contact is more preferable because of a good balance between initial irreversible capacity and high current density charge / discharge characteristics. Moreover, these carbon materials may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

Carbonaceous materials obtained by heat-treating the above-mentioned artificial carbonaceous materials and artificial graphite materials at least once in the range of 400 to 3200 ° C include coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, and oxidation of these pitches. Treated, needle coke, pitch coke and partially carbonized carbon agents, furnace black, acetylene black, pyrolytic products of organic materials such as pitch-based carbon fibers, carbonizable organic materials and their carbides, or carbonizable Examples thereof include solutions obtained by dissolving organic substances in low molecular organic solvents such as benzene, toluene, xylene, quinoline, n-hexane, and carbides thereof.

As the metal material used as the negative electrode active material (excluding lithium-titanium composite oxide), if lithium can be occluded / released, simple lithium, simple metal and alloy forming lithium alloy, or oxidation thereof Any of compounds such as oxides, carbides, nitrides, silicides, sulfides or phosphides may be used, and there is no particular limitation. The single metal and alloy forming the lithium alloy are preferably materials containing group 13 and group 14 metal / metalloid elements, more preferably aluminum, silicon and tin (hereinafter abbreviated as “specific metal elements”). ) Simple metals and alloys or compounds containing these atoms. These may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

As a negative electrode active material having at least one kind of atom selected from a specific metal element, a metal simple substance of any one specific metal element, an alloy composed of two or more specific metal elements, one type or two or more specific types Alloys comprising metal elements and one or more other metal elements, as well as compounds containing one or more specific metal elements, and oxides, carbides, nitrides and silicides of the compounds And composite compounds such as sulfides or phosphides. By using these simple metals, alloys or metal compounds as the negative electrode active material, the capacity of the battery can be increased.

In addition, a compound in which these complex compounds are complexly bonded to several kinds of elements such as a simple metal, an alloy, or a nonmetallic element is also included. Specifically, for example, in silicon and tin, an alloy of these elements and a metal that does not operate as a negative electrode can be used. For example, in the case of tin, 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 operate as a negative electrode, and a nonmetallic element may be used. 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) may be mentioned.
In addition, a composite material containing Si or Sn as the first constituent element and the second and third constituent elements in addition thereto can be given. The second constituent element is, for example, at least one of cobalt, iron, magnesium, titanium, vanadium, chromium, manganese, nickel, copper, zinc, gallium, and zirconium. For example, the third constituent element is at least one of boron, carbon, aluminum, and phosphorus.
In particular, since a high battery capacity and excellent battery characteristics can be obtained, as the metal material, a simple substance of silicon or tin (which may contain a small 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, and 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 occlude and release lithium, but a material containing titanium and lithium is preferable from the viewpoint of high current density charge / discharge characteristics, A lithium-containing composite metal oxide material containing titanium is more preferable, and a composite oxide of lithium and titanium (hereinafter abbreviated as “lithium titanium composite oxide”) is more preferable. That is, it is particularly preferable to use a lithium-titanium composite oxide having a spinel structure in a negative electrode active material for an electrolyte 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
[Wherein 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 preferable that it is a compound represented by these.
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 of a good balance of battery performance.

Particularly preferred representative compositions of the above compounds are Li _4/3 Ti _5/3 O ₄ in (i), Li ₁ Ti ₂ O ₄ in (ii), and Li _4/5 Ti _11/5 O in (iii). 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 mixture preferably further contains a binder, a thickener, and a conductive material.

As said binder, the thing similar to the binder which can be used for a positive electrode mentioned above is mentioned. 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. It is more preferably at most 10 mass%, further preferably at most 10 mass%, particularly preferably at most 8 mass%. When the ratio of the binder to the negative electrode active material exceeds the above range, the binder ratio in which the amount of the binder does not contribute to the battery capacity increases, and the battery capacity may be reduced. On the other hand, below the above range, the strength of the negative electrode may be reduced.

In particular, when the main component contains a rubbery polymer typified by SBR, 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 mass% or more is more preferable, and is usually 5 mass% or less, preferably 3 mass% or less, and more preferably 2 mass% or less. When the main component contains a fluorine-based polymer typified by polyvinylidene fluoride, the ratio to the negative electrode active material is usually 1% by mass or more, preferably 2% by mass or more, and more preferably 3% by mass or more. It is preferably 15% by mass or less, preferably 10% by mass or less, and more preferably 8% by mass or less.

As said thickener, the thing similar to the thickener which can be used for a positive electrode mentioned above is mentioned. 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, more preferably 0.6% by mass or more, and usually 5% by mass or less. 3 mass% or less is preferable and 2 mass% or less is more preferable. When the ratio of the thickener to the negative electrode active material is less than the above range, applicability may be significantly reduced. Moreover, when it exceeds the said range, the ratio of the negative electrode active material which occupies for a negative electrode active material layer will fall, and the problem that the capacity | capacitance of a battery falls and the resistance between negative electrode active materials may increase.

Examples of the conductive material for 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, the negative electrode active material, the binder, and the thickener and conductive material used as necessary can be dissolved or dispersed as long as it is a solvent. There is no restriction, and either an aqueous solvent or an organic solvent may be used.
Examples of the aqueous solvent include water and alcohol. Examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N- Examples include dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, and the like.

Examples of the material for the negative electrode current collector include copper, nickel, and stainless steel. 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 is 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, the above-described negative electrode material is added with the above-mentioned binder, thickener, conductive material, solvent, etc. to form a slurry, which is applied to a current collector, dried, pressed and densified. . In the case of using an alloy material, a method of forming the above-described thin film layer (negative electrode active material layer) containing the negative electrode active material by a technique such as vapor deposition, sputtering, or plating is also used.

The electrode structure when the negative electrode active material is made into an electrode is not particularly limited, but the density of the negative electrode active material present on the current collector is preferably 1 g · cm ⁻³ or more, and 1.2 g · cm ⁻³ or more. but more preferably, particularly preferably 1.3 g · ^{cm -3} or more, preferably 2.2 g · ^{cm -3} or less, more preferably 2.1 g · ^{cm -3} or less, 2.0 g · ^{cm -3} or less More preferred is 1.9 g · cm ⁻³ or less. If the density of the negative electrode active material present on the current collector exceeds the above range, the negative electrode active material particles are destroyed, increasing the initial irreversible capacity, or the electrolyte solution near the current collector / negative electrode active material interface In some cases, high current density charge / discharge characteristics are deteriorated due to a decrease in permeability. On the other hand, if the amount is less than the above range, the conductivity between the negative electrode active materials decreases, the battery resistance increases, 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. However, the thickness of the composite layer obtained by subtracting the thickness of the metal foil of the core is usually 15 μm or more, preferably 20 μm or more. More preferably, it is 30 μm or more, and usually 300 μm or less, preferably 280 μm or less, more preferably 250 μm or less.

Moreover, you may use what adhered the substance of the composition different from this to the surface of the said negative electrode plate. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate and carbonates such as lithium carbonate, calcium carbonate and magnesium carbonate.

<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 to the electrolytic solution and excellent in liquid retention, and known ones can be used. Among them, a resin, glass fiber, inorganic material, etc., formed of a material that is stable with respect to the electrolytic solution of the present invention is used, and a porous sheet or a nonwoven fabric-like material having excellent liquid retention properties is used. preferable.

As materials for the resin and glass fiber separator, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, glass filters and the like can be used. These materials, such as a polypropylene / polyethylene two-layer film and a polypropylene / polyethylene / polypropylene three-layer film, may be used alone or in combination of two or more in any combination and ratio. Especially, it is preferable that the said separator is the porous sheet | seat or nonwoven fabric etc. which use polyolefin, such as polyethylene and a polypropylene, from the point that the permeability of an electrolyte solution and a shutdown effect are favorable.

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, more preferably 30 μm or less. If the separator is too thin than the above range, the insulating properties and mechanical strength may decrease. On the other hand, if it is thicker than the above range, not only battery performance such as rate characteristics may be lowered, but also the energy density of the entire electrolyte battery may be lowered.

Furthermore, when using a porous material such as a porous sheet or nonwoven fabric as the separator, the porosity of the separator is arbitrary, but is usually 20% or more, preferably 35% or more, more preferably 45% or more, Further, it is usually 90% or less, preferably 85% or less, and more preferably 75% or less. If the porosity is too smaller than the above range, the membrane resistance tends to increase and the rate characteristics tend to deteriorate. Moreover, when larger than the said range, it exists in the tendency for the mechanical strength of a separator to fall and for insulation to fall.

Moreover, although the average pore diameter of a separator is also arbitrary, it is 0.5 micrometer or less normally, 0.2 micrometer or less is preferable, and it is 0.05 micrometer or more normally. If the average pore diameter exceeds the above range, a short circuit tends to occur. On the other hand, below the above range, the film resistance may increase and the rate characteristics may deteriorate.

On the other hand, as inorganic materials, 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. Used.

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

<Battery design>
The electrode group has a laminated structure in which the positive electrode plate and the negative electrode plate are interposed through the separator, and a structure in which the positive electrode plate and the negative electrode plate are wound in a spiral shape through the separator. Either is acceptable. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupation ratio) is usually 40% or more, preferably 50% or more, and usually 90% or less, preferably 80% or less. .

When the electrode group occupancy is below the above range, the battery capacity decreases. Also, if the above range is exceeded, the void space is small, the battery expands, and the member expands or the vapor pressure of the electrolyte liquid component increases and the internal pressure rises. In some cases, the gas release valve that lowers various characteristics such as storage at high temperature and the like, or releases the internal pressure to the outside is activated.

The current collecting structure is not particularly limited, but in order to more effectively realize the high current density charge / discharge characteristics by the electrolytic solution of the present invention, it is necessary to make the structure that reduces the resistance of the wiring part and the joint part. preferable. Thus, when internal resistance is reduced, the effect using the electrolyte solution of this invention is exhibited especially favorable.

In the case where the electrode group has the above laminated structure, a structure formed by bundling the metal core portions of the electrode layers and welding them to the terminals is preferably used. When the area of one electrode increases, the internal resistance increases. Therefore, it is also preferable to provide a plurality of terminals in the electrode to reduce the resistance. When the electrode group has the winding structure described above, the internal resistance can be lowered by providing a plurality of lead structures for the positive electrode and the negative electrode, respectively, and bundling the terminals.

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

In an exterior case using metals, the metal is welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed sealed structure, or a caulking structure using the above metals via a resin gasket. Things. Examples of the outer case using the laminate film include a case where a resin-sealed structure is formed by heat-sealing resin layers. In order to improve sealing performance, a resin different from the resin used for the laminate film may be interposed between the resin layers. In particular, when a resin layer is heat-sealed through a current collecting terminal to form a sealed structure, a metal and a resin are joined, so that a resin having a polar group or a modified group having a polar group introduced as an intervening resin is used. Resins are preferably used.

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

Moreover, the module provided with the lithium ion secondary battery of this invention is also one of this invention.

The lithium ion secondary battery also includes a positive electrode, a negative electrode, and the above-described electrolyte solution, and the positive electrode includes a positive electrode active material layer including a positive electrode current collector and a positive electrode active material, and the positive electrode active material Preferably contains Mn.

As the positive electrode active material, the formula: Li _a Mn _2-b M ¹ _b O ₄ (where 0.9 ≦ a; 0 ≦ b ≦ 1.5; M ¹ is Fe, Co, Ni, Cu, Zn) , Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and at least one metal selected from the group consisting of Si and Ge). Can be mentioned.
Among them, LiNi _0.5 Mn _1.5 O ₄ , LiMnO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Co _1/3 Mn are provided because they can provide a high-energy lithium ion secondary battery with high energy density. _{_{_{_{1/3 O 2, Li 1.2 Fe 0.4}}}} Mn 0.4 O 2, LiNi 0.5 Mn 0.5 O 2 is preferred.

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. Moreover, an upper limit becomes like this. Preferably it is 99 mass% or less, More preferably, it is 98 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. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

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

As the above-mentioned binder, any material can be used as long as it is a material that is safe with respect to the solvent and the electrolyte used in the production of the electrode. For example, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene , SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, NBR (Acrylonitrile-butadiene rubber), fluoro rubber, ethylene-propylene rubber, styrene / butadiene / styrene block copolymer or its hydrogenated product, EPDM (ethylene / propylene / diene terpolymer), styrene / ethylene / Tadiene / ethylene copolymer, styrene / isoprene / styrene block copolymer or hydrogenated product thereof, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer Examples thereof include polymers, fluorinated polyvinylidene fluoride, tetrafluoroethylene / ethylene copolymers, and polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions). In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

The lithium ion secondary battery also includes the above-described electrolytic solution, and a portion that is in contact with the electrolytic solution of the positive electrode current collector and a portion that is electrically connected to the positive electrode current collector is formed of a valve metal or an alloy thereof. It is preferable.

Examples of the valve metal include aluminum, titanium, tantalum, and chromium. More preferably, the positive electrode current collector is made of aluminum or an aluminum alloy.

In the lithium ion secondary battery, it is preferable that a portion in contact with the electrolytic solution in a portion electrically connected to the positive electrode current collector is also made of a valve metal or an alloy thereof. In particular, the battery outer case, and the lead wire and safety valve housed in the battery outer case, which are electrically connected to the positive electrode current collector and in contact with the non-aqueous electrolyte, are valve metal or It is preferable to comprise the alloy. Stainless steel coated with a valve metal or an alloy thereof may be used.

The electric double layer capacitor may include a positive electrode, a negative electrode, and the electrolytic solution described above.
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 nonpolarizable electrode.

The polarizable electrode mainly composed of activated carbon used in the present invention preferably contains a non-activated carbon having a large specific surface area and a conductive agent such as carbon black imparting electron conductivity. The polarizable electrode can be formed by various methods. For example, a polarizable 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 in an inert gas atmosphere and a water vapor atmosphere after press molding. Preferably, the polarizable electrode is joined 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, formed into a sheet, and dried to form a polarizable electrode. For example, polytetrafluoroethylene is used as the binder. In addition, activated carbon powder, carbon black, binder and solvent are mixed to form a slurry, and this slurry is coated on the metal foil of the current collector and dried to obtain a polarizable electrode integrated with the current collector. it can.

An electric double layer capacitor may be formed by using a polarizable electrode mainly composed of activated carbon for both electrodes, but a configuration using a non-polarizable 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 structure combining a polarizable electrode negative electrode mainly composed of carbon, a negative electrode mainly composed of a carbon material capable of reversibly occluding and releasing lithium ions, or a negative electrode composed mainly of lithium metal or lithium alloy and activated carbon. A configuration combining a positive electrode with a polarity is also possible.

Further, carbonaceous materials such as carbon black, graphite, expanded graphite, porous carbon, carbon nanotube, carbon nanohorn, and ketjen black may be used instead of or in combination with activated carbon.

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

Solvents used to prepare the slurry for electrode preparation are preferably those that dissolve the binder. Depending on the type of binder, N-methylpyrrolidone, dimethylformamide, toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methyl acetate, phthalate Dimethyl acid, ethanol, methanol, butanol or water is appropriately selected.

Examples of the activated carbon used for the polarizable electrode include phenol resin-based activated carbon, coconut-based activated carbon, and petroleum coke-based activated carbon. Among these, it is preferable to use petroleum coke activated carbon or phenol resin activated carbon in that a large capacity can be obtained. Activated carbon activation treatment methods include a steam activation treatment method, a molten KOH activation treatment method, and the like, and it is preferable to use activated carbon obtained by a molten KOH activation treatment method in terms of obtaining a larger capacity.

Preferred conductive agents used for the polarizable 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 polarizable electrode is so as to obtain good conductivity (low internal resistance), and if it is too large, the product capacity is reduced. It is preferable to set it as 50 mass%.

As the activated carbon used for the polarizable 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 a low internal resistance can be obtained. Is preferred. Further, as a preferable carbon material for constituting an electrode mainly composed of a carbon material capable of reversibly inserting and extracting lithium ions, natural graphite, artificial graphite, graphitized mesocarbon spherule, graphitized whisker, gas layer Examples thereof include a grown carbon fiber, a fired product of furfuryl alcohol resin, and a fired product of novolac resin.

The current collector is only required to be chemically and electrochemically corrosion resistant. As the current collector of the polarizable electrode mainly composed of activated carbon, stainless steel, aluminum, titanium or tantalum can be preferably used. Of these, stainless steel or aluminum is a particularly preferable material in terms of both characteristics and cost of the obtained electric double layer capacitor. As the current collector of the electrode mainly composed of a carbon material capable of reversibly inserting and extracting lithium ions, stainless steel, copper or nickel is preferably used.

In addition, in order to preliminarily store lithium ions in a carbon material capable of reversibly inserting and extracting lithium ions, (1) mixing powdered lithium with a carbon material capable of reversibly inserting and extracting lithium ions. (2) A lithium foil is placed on an electrode formed of a carbon material capable of reversibly occluding and releasing lithium ions and a binder, and the electrode is in contact with the lithium salt. A method in which lithium is ionized by immersing it in an electrolyte solution in which lithium is ionized and lithium ions are taken into the carbon material; (3) formed by a carbon material and a binder capable of reversibly inserting and extracting lithium ions; Place the electrode on the negative side, place lithium metal on the positive side, immerse it in a non-aqueous electrolyte containing lithium salt as an electrolyte, and pass an electric current to make an electrochemical carbon material A method of incorporating in a state in which lithium has been ionized.

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

For example, in a wound electric double layer capacitor, a positive electrode and a negative electrode made of a laminate (electrode) of a current collector and an electrode layer are wound through a separator to produce a wound element, and the wound element is made of aluminum. And then filled with an electrolytic solution, preferably a non-aqueous electrolytic solution, and then sealed and sealed with a rubber sealing body.

As the separator, conventionally known materials and structures can be used. For example, a polyethylene porous membrane, polypropylene fiber, glass fiber, cellulose fiber non-woven fabric and the like can be mentioned.

In addition, by a known method, a laminate type electric double layer capacitor in which a sheet-like positive electrode and a negative electrode are laminated via an electrolytic solution and a separator, and a positive electrode and a negative electrode are formed into a coin shape by fixing with a gasket and the electrolytic solution and the separator. A configured coin type electric double layer capacitor can also be used.

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

Examples and Comparative Examples (Preparation of Electrolytic Solution)
A solvent and an acid anhydride were mixed so that the composition described in Table 1 was obtained, and LiPF ₆ was added thereto to a concentration of 1.0 mol / liter to obtain a nonaqueous electrolytic solution. The blending ratio of the acid anhydride was expressed by mass% with respect to the electrolytic solution after blending the acid anhydride.

The compounds in the table are as follows.

a: Dimethyl carbonate b: CH ₃ OCOOCH ₂ CF ₃
_{_{_{c: CH 3 OCOOCH 2 CF 2}}} H
d: propylene carbonate e: ethylene carbonate f: trifluoromethyl ethylene carbonate g: difluoromethyl ethylene carbonate h: monofluoroethylene carbonate

(Production of coin-type lithium ion secondary battery)
LiNi _0.5 Mn _1.5 O ₄ , carbon black and polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., trade name: KF-7200) were mixed at 92/3/5 (mass ratio), and N-methyl- A positive electrode mixture slurry was prepared by dispersing in 2-pyrrolidone to form a slurry. The obtained positive electrode mixture slurry is uniformly coated on an aluminum current collector, dried to form a positive electrode active material layer (thickness 50 μm), and then compression molded by a roller press machine to form a positive electrode laminate. Manufactured. The positive electrode laminate was punched to a size of 1.6 cm in diameter with a punching machine to produce a circular positive electrode.

Separately, a negative electrode current collector (thickness 10 μm) was prepared by adding styrene-butadiene rubber dispersed in distilled water to artificial graphite powder to a solid content of 6% by mass and mixing with a disperser to form a slurry. On the copper foil) and dried to form a negative electrode active material layer. Thereafter, it was compression-molded with a roller press and punched into a diameter of 1.6 cm with a punch to produce a circular negative electrode.

The positive electrode was housed in a stainless steel positive electrode can, and a 20 μm microporous polyethylene film (separator) impregnated with the nonaqueous electrolyte solution and the negative electrode were sequentially placed thereon. The positive electrode can and the stainless steel sealing plate were caulked and sealed through an insulating gasket to produce a coin-type lithium ion battery.

(Remaining capacity maintenance rate)
Charging / discharging is performed under predetermined charging / discharging conditions (charging at 0.5C and 4.85V until the charging current becomes 1 / 10C and discharging to 3.0V at a current equivalent to 0.5C) Examined. Then, it charged again on said charging conditions, and preserve | saved for 24 hours in a 85 degreeC thermostat. The battery after storage was discharged at 25 ° C. under the above discharge conditions to a discharge end voltage of 3 V, and the remaining capacity was measured. The remaining capacity retention rate was determined by the following formula. The results are shown in Table 1.
Remaining capacity retention rate (%) = remaining capacity / discharge capacity before storage at high temperature × 100

Claims

General formula (1):

(In the formula, ring A is a saturated or unsaturated hydrocarbon ring having 3 to 8 carbon atoms, or a saturated or unsaturated heterocyclic ring having 3 to 8 carbon atoms, which may have a substituent. And an acid anhydride (1) represented by the formula (1), which may be monocyclic or polycyclic).
The electrolytic solution according to claim 1, comprising 0.001 to 5 mass% of an acid anhydride (1) with respect to the electrolytic solution.
Further, a solvent is included, and the solvent has the general formula (2):

(Wherein Rf 21 is —F, —CHF 2 or —CF 3 , R 21 , R 24 and R 25 are the same or different, and —H, —F, —CH 3 , —CHF 2 or —CF 3, R 22 and R 23 are the same or different, -H, -F, -CH 3, -CHF 2 or -CF 3, or both, carbon atoms and R 23 which R 22 is attached is 3. The electrolytic solution according to claim 1, comprising a fluorinated carbonate (2) represented by a single bond that forms a ring by bonding to bonded carbon atoms.
An electrochemical device comprising the electrolytic solution according to claim 1, 2 or 3.
A lithium ion secondary battery comprising the electrolytic solution according to claim 1, 2 or 3.
A module comprising the electrochemical device according to claim 4 or the lithium ion secondary battery according to claim 5.