WO2026042425A1 - Composition for electrolyte solution, electrochemical device, secondary battery, and lithium-ion secondary battery - Google Patents

Abstract

The present disclosure provides: a composition for an electrolyte solution, which can suppress gas generation during high-temperature storage; and an electrochemical device, a secondary battery and a lithium-ion secondary battery, each of which uses this composition for an electrolyte solution. More specifically, the present disclosure is a composition for an electrolyte solution, wherein the composition contains a compound (A) represented by formula (A). (A) Rf¹-O-CH₂-CH₂-O-R¹ (In the formula, Rf¹ is 1-6 C fluoroalkyl group, and R¹ is H, Li, Na, K or Cs).

Description

Electrolyte composition, electrochemical device, secondary battery, and lithium ion secondary battery

This disclosure relates to electrolyte compositions, electrochemical devices, secondary batteries, and lithium-ion secondary batteries.

In recent years, with the trend toward lighter and smaller electrical appliances, the development of electrochemical devices such as lithium-ion secondary batteries with high energy density has progressed. Furthermore, as the range of applications for electrochemical devices such as lithium-ion secondary batteries expands, there is a demand for improved performance. In particular, improving battery performance will become increasingly important as lithium-ion secondary batteries are used in vehicles in the future.

Patent Document 1 describes an electrolyte solution for lithium metal secondary batteries that contains a specific lithium salt and a non-aqueous solvent.

Special Publication No. 2022-552481

The present disclosure aims to provide an electrolyte composition that can suppress gas generation during high-temperature storage, as well as electrochemical devices, secondary batteries, and lithium-ion secondary batteries that use the electrolyte composition.

The present disclosure (1) is a composition for an electrolyte solution containing a compound (A) represented by the following formula (A):
(A) Rf ¹ -O-CH ₂ -CH ₂ -O-R ¹
(In the formula, ^Rf1 is a fluoroalkyl group having 1 to 6 carbon atoms, and ^R1 is H, Li, Na, K, or Cs.)

The present disclosure (2) relates to the Rf ¹ .
HCF ₂ -CF ₂ -,
HCF ₂ -CF ₂ -CH ₂ -,
HCF ₂ -CH ₂ -,
CF ₃ —CF ₂ —CH ₂ —, or
The electrolyte composition according to the present disclosure (1) is CF ₃ —CHF—CF ₂ —.

The present disclosure (3) is the composition for an electrolyte solution according to the present disclosure (1) or (2), wherein R ¹ is H or Li.

The present disclosure (4) is a composition for an electrolyte solution according to any one of the present disclosures (1) to (3), in which the content of the compound (A) is 0.0001 to 30,000 ppm relative to the composition for an electrolyte solution.

The present disclosure (5) provides that the compound (A) is
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OH,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OLi,
CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OH, and
In the composition for an electrolyte solution according to any one of the present disclosures (1) to (4), the electrolyte is at least one selected from the group consisting of CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OLi.

The present disclosure (6) is a composition for an electrolyte solution according to any one of the present disclosures (1) to (5), which contains a fluorinated ether (E) represented by the following formula (E):
(E) Rf ² -O-R ²
(In the formula, ^Rf2 is a fluoroalkyl group having 1 to 5 carbon atoms, and ^R2 is H or an alkyl group having 1 to 6 carbon atoms. The alkyl group of ^R2 may have an ether bond and/or fluorine.)

The present disclosure (7) is the composition for an electrolyte solution according to the present disclosure (6), wherein Rf ² is HCF ₂ —CF ₂ —.

The present disclosure (8) relates to the R ² ,
—CH ₂ —CH ₂ —O—CF ₂ —CF ₂ H, or
-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃
The composition for an electrolyte solution according to the present disclosure (6) or (7),

The present disclosure (9) provides that the fluorinated ether (E) is
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H, and
CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃
The composition for an electrolyte solution according to any one of the present disclosures (6) to (8) is at least one selected from the group consisting of:

The present disclosure (10) is a composition for an electrolyte solution according to any one of the present disclosures (6) to (9), in which the content of the fluorinated ether (E) is 0.01 to 99 mass% relative to the composition for an electrolyte solution.

The present disclosure (11) is a composition for an electrolyte solution according to any one of the present disclosures (1) to (10), which contains at least one lithium salt selected from the group consisting of LiPF ₆ , LiFSI, and LiTFSI.

The present disclosure (12) relates to the compound (A),
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OH,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OLi,
CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OH, and
at least one selected from the group consisting of CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OLi;
the content of the compound (A) is 0.003 to 30,000 ppm relative to the electrolyte solution composition;
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H, and
CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃
At least one fluorinated ether (E) selected from the group consisting of:
The composition for an electrolyte solution according to any one of the present disclosures (1) to (11), wherein the content of the fluorinated ether (E) is 0.5 to 50 mass % relative to the composition for an electrolyte solution.

The present disclosure (13) relates to a secondary battery comprising the electrolyte solution composition described in the present disclosure (12) and lithium metal as the negative electrode active material.

The present disclosure (14) relates to compound (A),
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OH,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OLi,
CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OH, and
at least one selected from the group consisting of CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OLi;
the content of the compound (A) is 0.01 to 30,000 ppm relative to the electrolyte solution composition;
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H, and
CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃
At least one fluorinated ether (E) selected from the group consisting of:
The composition for an electrolyte solution according to any one of the present disclosures (1) to (11), wherein the content of the fluorinated ether (E) is 40 to 95 mass % relative to the composition for an electrolyte solution.

The present disclosure (15) relates to a secondary battery comprising the electrolyte solution composition described in the present disclosure (14) and a silicon material as a negative electrode active material.

The present disclosure (16) is an electrolyte composition described in any one of the present disclosures (1) to (12) and (14) for use in a secondary battery.

The present disclosure (17) is an electrochemical device comprising the electrolyte solution composition described in any one of the present disclosures (1) to (12) and (14).

The present disclosure (18) is a secondary battery containing the electrolyte solution composition described in any one of the present disclosures (1) to (12) and (14).

The present disclosure (19) is a lithium ion secondary battery containing the electrolyte solution composition described in any one of the present disclosures (1) to (12) and (14).

The present disclosure provides an electrolyte solution composition that can suppress gas generation during high-temperature storage, as well as electrochemical devices, secondary batteries, and lithium-ion secondary batteries that use the electrolyte solution composition.

This disclosure is explained in detail below.

The present disclosure relates to a composition for an electrolyte solution containing a compound (A) represented by the following formula (A):
(A) Rf ¹ -O-CH ₂ -CH ₂ -O-R ¹
(In the formula, ^Rf1 is a fluoroalkyl group having 1 to 6 carbon atoms, and ^R1 is H, Li, Na, K, or Cs.)

By containing compound (A), the composition of the present disclosure can suppress gas generation during high-temperature storage in electrochemical devices. This effect is presumably achieved by compound (A) being adsorbed to defective sites in the positive electrode, thereby suppressing side reactions at the positive electrode/electrolyte interface.

The composition of the present disclosure is used in an electrolyte solution, and may be either an electrolyte solution or a constituent component (additive, etc.) of an electrolyte solution.
Furthermore, the composition of the present disclosure can be suitably used in electrochemical devices (particularly secondary batteries such as lithium ion secondary batteries).

In formula (A), Rf ¹ is a fluoroalkyl group having 1 to 6 carbon atoms.
The number of carbon atoms in the fluoroalkyl group is preferably 1 to 4, more preferably 1 to 3, still more preferably 2 or 3, and particularly preferably 2. The fluoroalkyl group may be linear or branched, but is preferably linear.
Rf ¹ is preferably HCF ₂ —CF ₂ —, HCF ₂ —CF ₂ —CH ₂ —, HCF ₂ —CH ₂ —, CF ₃ —CF ₂ —CH ₂ —, or CF ₃ —CHF—CF ₂ —, and more preferably HCF ₂ —CF ₂ — or CF ₃ —CHF—CF ₂ — from the viewpoint of suppressing gas generation during high-temperature storage.

In formula (A), R ¹ represents H, Li, Na, K, or Cs. From the viewpoint of suppressing gas generation during high-temperature storage, H, Li, Na, and K are preferred, and H and Li are more preferred.

Among these, the compound (A) is preferably HCF ₂ —CF ₂ —O—CH ₂ —CH ₂ —OH, from the viewpoint of suppressing gas generation during high-temperature storage.
HCF ₂ -CF ₂ -CH ₂ -O-CH ₂ -CH ₂ -OH,
HCF ₂ -CH ₂ -O-CH ₂ -CH ₂ -OH,
_CF3 - _CF2 - _CH2 -O- _CH2 - _CH2 -OH,
_CF3- CHF- _CF2 -O- _CH2 - _CH2- OH,
CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -OLi,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OLi,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OK,
is preferred,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OH,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OLi,
_CF3- CHF- _CF2 -O- _CH2 - _CH2- OH,
CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -OLi,
is more preferred,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OH,
_CF3- CHF- _CF2 -O- _CH2 - _CH2- OH,
is more preferred.

Compound (A) may be used alone or in combination of two or more types.

In the composition of the present disclosure, the content of compound (A) is preferably 0.0001 ppm or more and 30,000 ppm or less relative to the composition of the present disclosure. In order to further suppress gas generation during high-temperature storage, the content of compound (A) is more preferably 0.003 ppm or more relative to the composition of the present disclosure, even more preferably 0.01 ppm or more, and particularly preferably 0.1 ppm or more, and more preferably 20,000 ppm or less, even more preferably 10,000 ppm or less, even more preferably 7,000 ppm or less, and particularly preferably 5,000 ppm or less.

The composition of the present disclosure preferably contains a fluorinated ether (E) represented by the following formula (E):
(E) Rf ² -O-R ²
(In the formula, ^Rf2 is a fluoroalkyl group having 1 to 5 carbon atoms, and ^R2 is H or an alkyl group having 1 to 6 carbon atoms. The alkyl group of ^R2 may have an ether bond and/or fluorine.)

By using compound (A) and fluorinated ether (E) in combination, gas generation during high-temperature storage can be further suppressed. This effect is presumably achieved by suppressing side reactions at the positive electrode/electrolyte interface due to the high oxidation resistance of fluorinated ether (E) and the adsorption of compound (A) to the positive electrode.

In formula (E), ^Rf2 is a fluoroalkyl group having 1 to 6 carbon atoms.
The number of carbon atoms in the fluoroalkyl group is preferably 1 to 4, more preferably 1 to 3, still more preferably 1 or 2, and particularly preferably 2. The fluoroalkyl group may be linear or branched, but is preferably linear.
Rf ² is preferably CF ₃ -, CF ₂ H-, CFH ₂ -, CF ₃ -CF ₂ -, CF ₃ -CH ₂ -, HCF ₂ -CH ₂ -, HCF ₂ -CF ₂ -, FCH ₂ -CH ₂ -, CF ₃ -CH ₂ -CH ₂ -, CF ₃ -CF ₂ -CH ₂ -, HCF ₂ -CF ₂ -CH ₂ -, FCH ₂ -CF ₂ -CH ₂ -, HCF ₂ -CF ₂ -CF ₂ -CF ₂ -CH ₂ -, and more preferably HCF ₂ -CF ₂ - from the viewpoint of suppressing gas generation during high temperature storage.

In formula (E), ^R2 is H or an alkyl group having 1 to 6 carbon atoms.
The number of carbon atoms in the alkyl group is preferably 1 to 4, more preferably 1 to 3, and even more preferably 3. The alkyl group may be linear or branched, but is preferably linear. The alkyl group may have an ether bond and/or fluorine, but preferably has an ether bond and fluorine.
R ² is -CF ₃ , -CF ₂ H, -CFH ₂ , -CH ₃ , -CH ₂ -CH ₃ , -CF ₂ -CF ₃ , -CH ₂ -CF ₃ , -CH ₂ -CF ₂ H, -CH ₂ -CFH ₂ , -CH ₂ -CH ₂ -CH ₃ , -CH ₂ -CH ₂ -CF ₃ , -CH ₂ -CF ₂ -CF ₃ , -CH ₂ -CF ₂ -CF ₂ H, -CH ₂ -CF ₂ -CFH ₂ , -CH ₂ -CF ₂ -CF ₂ -CF ₂ -CF ₂ H, -CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H, -CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃ is preferred, and from the viewpoint of suppressing gas generation during high temperature storage, -CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H and -CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃ are more preferred.

As the fluorinated ether (E), among others, HCF ₂ —CF ₂ —O—CH ₂ —CF ₂ —O—CF ₂ —CF ₂ H,
HCF ₂ -CF ₂ -CH ₂ -O-CH ₂ -CH ₂ -CH ₂ -CF ₂ -CF ₂ H,
HCF ₂ -CH ₂ -O-CH ₂ -CH ₂ -O-CH ₂ -CF ₂ H,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H,
CF ₃ -CF ₂ -CH ₂ -O-CH ₂ -CH ₂ -O-CH ₂ -CF ₂ -CF ₃ ,
CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃ ,
HCF ₂ -CF ₂ -CH ₂ -O-CF ₂ -CF ₂ H,
is preferred,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H,
CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃ ,
is more preferred.

The fluorinated ether (E) may be used alone or in combination of two or more kinds.
When two kinds of fluorinated ethers (E) are used in combination, it is preferable to combine HCF ₂ —CF ₂ —O—CH ₂ —CH ₂ —O—CF ₂ —CF ₂ H with HCF ₂ —CF ₂ —CH ₂ —O—CF ₂ —CF ₂ H.

In the composition of the present disclosure, the content of the fluorinated ether (E) is preferably 0.01% by mass or more and 99% by mass or less, based on the composition of the present disclosure.
When the composition of the present disclosure is used in a secondary battery containing a silicon material as a negative electrode active material, the content of the fluorinated ether (E) relative to the composition of the present disclosure is more preferably 10% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more, and is more preferably 95% by mass or less, even more preferably 90% by mass or less, even more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less, in order to further suppress gas generation during high-temperature storage.
When the composition of the present disclosure is used in a secondary battery containing a metal material (particularly lithium metal) as a negative electrode active material, the content of the fluorinated ether (E) relative to the composition of the present disclosure is more preferably 0.5% by mass or more, even more preferably 2% by mass or more, even more preferably 10% by mass or more, and particularly preferably 20% by mass or more, and is more preferably 80% by mass or less, even more preferably 70% by mass or less, even more preferably 60% by mass or less, and particularly preferably 50% by mass or less, in order to further suppress gas generation during high-temperature storage.

In the composition of the present disclosure, the content of the compound (A) is preferably 0.00000001% by mass or more and 5% by mass or less relative to the content of the fluorinated ether (E).
When the composition of the present disclosure is used as a negative electrode active material in a secondary battery containing a silicon material, the content of compound (A) relative to the content of fluorinated ether (E) is more preferably 0.0000001% by mass or more, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.06% by mass or less, and particularly preferably 0.03% by mass or less, in order to further suppress gas generation during high-temperature storage.
When the composition of the present disclosure is used as a negative electrode active material in a secondary battery containing a metal material (particularly lithium metal), the content of compound (A) relative to the content of fluorinated ether (E) is more preferably 0.00000003% by mass or more, even more preferably 0.0000003% by mass or more, and is more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and particularly preferably 0.05% by mass or less, in order to further suppress gas generation during high-temperature storage.

The composition of the present disclosure preferably contains a solvent. The fluorinated ether (E) can be used as the solvent, but the composition may also contain a solvent other than the fluorinated ether (E).

It is preferable that the above solvent contains at least one selected from the group consisting of carbonates and carboxylic acid esters.

The carbonate may be a cyclic carbonate or a chain carbonate.

The above-mentioned cyclic carbonate may be a non-fluorinated cyclic carbonate or a fluorinated cyclic carbonate.

The non-fluorinated cyclic carbonate may be a non-fluorinated saturated cyclic carbonate, preferably a non-fluorinated saturated alkylene carbonate having an alkylene group with 2 to 6 carbon atoms, and more preferably a non-fluorinated saturated alkylene carbonate having an alkylene group with 2 to 4 carbon atoms.

Among these, the non-fluorinated saturated cyclic carbonate is preferably at least one selected from the group consisting of ethylene carbonate, propylene carbonate, cis-2,3-pentylene carbonate, cis-2,3-butylene carbonate, 2,3-pentylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 1,2-butylene carbonate, and butylene carbonate, as these have a high dielectric constant and favorable viscosity.

The above non-fluorinated saturated cyclic carbonates may be used alone or in any combination and ratio of two or more.

When the non-fluorinated saturated cyclic carbonate is included, the content of the non-fluorinated saturated cyclic carbonate relative to the solvent is preferably 5 to 90% by volume, more preferably 10 to 60% by volume, and even more preferably 15 to 45% by volume.

The fluorinated cyclic carbonate is a cyclic carbonate having a fluorine atom. A solvent containing the fluorinated cyclic carbonate can be suitably used even under high voltage.
In this specification, the term "high voltage" refers to a voltage of 4.2 V or higher. The upper limit of the "high voltage" is preferably 5.5 V, and more preferably 5.0 V.

The above-mentioned fluorinated cyclic carbonate may be a fluorinated saturated cyclic carbonate or a fluorinated unsaturated cyclic carbonate.

The above-mentioned fluorinated saturated cyclic carbonate is a saturated cyclic carbonate containing a fluorine atom, specifically represented by the following general formula (A):

(wherein X ¹ to X ⁴ are the same or different and each represent -H, -CH ₃ , -C ₂ H ₅ , -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond, provided that at least one of X ¹ to X ⁴ is -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond.) Examples of the fluorinated alkyl group include -CF ₃ , -CF ₂ H, -CH ₂ F, etc.

When the composition of the present disclosure contains the above-mentioned fluorinated saturated cyclic carbonate, the oxidation resistance of the electrolyte is improved and stable and excellent charge/discharge characteristics are obtained when the composition is applied to a high-voltage lithium ion secondary battery or the like.
In this specification, an "ether bond" is a bond represented by --O--.

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

X ¹ to X ⁴ are preferably —H, —F, a fluorinated alkyl group (a), a fluorinated alkyl group having an ether bond (b), or a fluorinated alkoxy group (c), because this is expected to reduce viscosity at low temperatures, increase the flash point, and further improve the solubility of the electrolyte salt.

The fluorinated alkyl group (a) is an alkyl group in which at least one hydrogen atom has been substituted with a fluorine atom. The fluorinated alkyl group (a) preferably has 1 to 20 carbon atoms, more preferably 1 to 17 carbon atoms, still more preferably 1 to 7 carbon atoms, and particularly preferably 1 to 5 carbon atoms.
If the number of carbon atoms is too large, there is a risk that the low-temperature characteristics and the solubility of the electrolyte salt may be reduced, whereas if the number of carbon atoms is too small, there may be a reduction in the solubility of the electrolyte salt, a reduction in discharge efficiency, and even an increase in viscosity.

Among the above fluorinated alkyl groups (a), those having one carbon atom include CFH ₂ —, CF ₂ H— and CF ₃ —. In particular, CF ₂ H— or CF ₃ — is preferred in terms of high-temperature storage properties, with CF ₃ — being most preferred.

The above-mentioned fluorinated chain carbonates may be used alone or in any combination and ratio of two or more.

When the fluorinated chain carbonate is included, the content of the fluorinated chain carbonate is preferably 10 to 90% by mass, more preferably 40 to 85% by mass, and even more preferably 50 to 80% by mass, relative to the composition.

The above-mentioned fluorinated chain carbonate is a chain carbonate containing fluorine atoms. Solvents containing fluorinated chain carbonates can be suitably used even under high voltage.

The fluorinated chain carbonate may be a fluorinated chain carbonate represented by the general formula (B):
Rf ² OCOOR ⁷ (B)
(wherein ^Rf2 is a fluorinated alkyl group having 1 to 7 carbon atoms, and ^R7 is an alkyl group having 1 to 7 carbon atoms which may contain a fluorine atom)

^Rf2 is a fluorinated alkyl group having 1 to 7 carbon atoms, and ^R7 is an alkyl group having 1 to 7 carbon atoms which may contain a fluorine atom.
The fluorinated alkyl group is an alkyl group in which at least one hydrogen atom has been substituted with a fluorine atom. When ^R7 is an alkyl group containing a fluorine atom, it becomes a fluorinated alkyl group.
^Rf2 and ^R7 preferably have 1 to 7 carbon atoms, more preferably 1 or 2, in terms of low viscosity.
If the number of carbon atoms is too large, there is a risk that the low-temperature characteristics and the solubility of the electrolyte salt may be reduced, whereas if the number of carbon atoms is too small, there may be a reduction in the solubility of the electrolyte salt, a reduction in discharge efficiency, and even an increase in viscosity.

Examples of the fluorinated alkyl group having one carbon atom include CFH ₂ —, CF ₂ H—, CF ₃ —, etc. In particular, CFH ₂ — or CF ₃ — is preferred in terms of high-temperature storage properties.

The fluorinated alkyl group having two or more carbon atoms includes a group represented by the following general formula (d-1):
R ^d1 -R ^d2 - (d-1)
(wherein R ^d1 is an alkyl group having 1 or more carbon atoms which may have a fluorine atom; R ^d2 is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom; provided that at least one of R ^d1 and R ^d2 has a fluorine atom) is a preferred example from the viewpoint of good solubility of the electrolyte salt.
R ^d1 and R ^d2 may further have atoms other than carbon atoms, hydrogen atoms and fluorine atoms.

R ^d1 is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. ^{R d1} is preferably a linear or branched alkyl group having 1 to 6 carbon atoms. The number of carbon atoms in ^{R d1} is more preferably 1 to 3.

Specific examples of preferred fluorinated alkyl groups include CF ₃ CF ₂ —, HCF ₂ CF ₂ —, H ₂ CFCF ₂ —, CH ₃ CF ₂ —, CF ₃ CH ₂ —, CF 3 CF ₂ CF ₂ —, HCF ₂ CF ₂ CF _{2 —} , H ₂ CFCF ₂ CF ₂ —, CH ₃ CF ₂ CF ₂ —,

Among these, the fluorinated alkyl groups of Rf ² and R ⁷ are preferably CF ₃ -, CF ₃ CF ₂ -, (CF ₃ ) ₂ CH-, CF ₃ CH ₂ -, C ₂ F ₅ CH ₂ -, CF ₃ CF ₂ CH ₂ -, HCF ₂ CF ₂ CH ₂ -, CF ₃ CFHCF ₂ CH ₂ -, CFH ₂ - and CF ₂ H-, and from the viewpoints of high flame retardancy and good rate characteristics and oxidation resistance, CF ₃ CH ₂ -, CF ₃ CF ₂ CH ₂ -, HCF ₂ CF ₂ CH ₂ -, CFH ₂ - and CF ₂ H- are more preferred.

When ^R7 is an alkyl group containing no fluorine atoms, it is an alkyl group having 1 to 7 carbon atoms. In terms of low viscosity, ^R7 preferably has 1 to 4 carbon atoms, and more preferably has 1 to 3 carbon atoms.

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 —, etc. Among 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 15 to 70% by mass. When the fluorine content is within the above range, compatibility with solvents and salt solubility can be maintained. The fluorine content is more preferably 20% by mass or more, even more preferably 30% by mass or more, and particularly preferably 35% by mass or more, and more preferably 60% by mass or less, and even more preferably 50% by mass or less.
In the present disclosure, the fluorine content is determined based on the structural formula of the fluorinated chain carbonate as follows:
{(number of fluorine atoms×19)/molecular weight of fluorinated chain carbonate}×100(%)
This is the value calculated by

The above-mentioned fluorinated chain carbonate is preferably one of the following compounds, as they have low viscosity.

As the fluorinated chain carbonate, methyl 2,2,2-trifluoroethyl carbonate (F ₃ CH ₂ COC(═O)OCH ₃ ) is particularly preferred.

The above-mentioned fluorinated chain carbonates may be used alone or in any combination and ratio of two or more.

When the fluorinated chain carbonate is included, the content of the fluorinated chain carbonate relative to the solvent is preferably 10 to 90% by volume, more preferably 40 to 85% by volume, and even more preferably 50 to 80% by volume.

The solvent preferably contains at least one selected from the group consisting of the cyclic carbonate, the chain carbonate, and the chain carboxylic acid ester, and more preferably contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester. The cyclic carbonate is preferably a saturated cyclic carbonate.
A composition containing the solvent having the above composition can further suppress gas generation during high-temperature storage of an electrochemical device.

When the solvent contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester, the total amount of the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester is preferably 10 to 100% by mass, more preferably 30 to 100% by mass, and even more preferably 50 to 100% by mass, based on the composition.

When the solvent contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester, the mass ratio of the cyclic carbonate to the at least one selected from the group consisting of the chain carbonate and the chain carboxylic acid ester is preferably 5/95 to 95/5, more preferably 10/90 or more, even more preferably 15/85 or more, particularly preferably 20/80 or more, more preferably 90/10 or less, even more preferably 60/40 or less, and particularly preferably 50/50 or less.

The solvent also preferably contains at least one selected from the group consisting of the non-fluorinated saturated cyclic carbonate, the non-fluorinated chain carbonate, and the non-fluorinated chain carboxylic acid ester, and more preferably contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester. An electrolyte solution containing a solvent of the above composition can be suitably used in electrochemical devices used at relatively low voltages.

When the solvent contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester, the total amount of the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester is preferably 5 to 100% by mass, more preferably 20 to 100% by mass, and even more preferably 30 to 100% by mass, relative to the composition.

When the solvent contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester, the mass ratio of the non-fluorinated saturated cyclic carbonate to the at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester is preferably 5/95 to 95/5, more preferably 10/90 or more, even more preferably 15/85 or more, particularly preferably 20/80 or more, more preferably 90/10 or less, even more preferably 60/40 or less, and particularly preferably 50/50 or less.

The solvent also preferably contains at least one selected from the group consisting of the fluorinated saturated cyclic carbonate, the fluorinated chain carbonate, and the fluorinated chain carboxylic acid ester, and more preferably contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester. An electrolyte solution containing a solvent of the above composition can be suitably used not only in electrochemical devices used at relatively low voltages, but also in electrochemical devices used at relatively high voltages.

When the solvent contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester, the total amount of the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester is preferably 10 to 100% by mass, more preferably 30 to 100% by mass, and even more preferably 50 to 100% by mass, based on the composition.

When the solvent contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester, the mass ratio of the fluorinated saturated cyclic carbonate to the at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylic acid ester is preferably 5/95 to 95/5, more preferably 10/90 or more, even more preferably 15/85 or more, particularly preferably 20/80 or more, more preferably 90/10 or less, even more preferably 60/40 or less, and particularly preferably 50/50 or less.

The solvent is preferably a non-aqueous solvent, and the composition of the present disclosure is preferably a composition for a non-aqueous electrolyte solution.
The content of the solvent in the electrolytic solution is preferably 70 to 99.999% by mass, more preferably 80% by mass or more, and more preferably 92% by mass or less.

The composition of the present disclosure preferably further contains an electrolyte salt. The electrolyte salt may be any salt that can be used in an electrolytic solution, such as lithium salt, ammonium salt, metal salt, liquid salt (ionic liquid), inorganic polymer salt, or organic polymer salt.

The electrolyte salt of the electrolyte solution for lithium ion secondary batteries is preferably a lithium salt.
Any lithium salt can be used, and specific examples thereof include the following: inorganic _lithium salts such as _LiPF6 , _LiBF4 , _LiClO4 , _LiAlF4 , _LiSbF6 , _LiTaF6 , _LiWF7 , LiAsF6, _LiAlCl4 , LiI, LiBr, _LiCl , _{LiB10Cl10 , Li2SiF6} , _Li2PFO3 , _{and LiPO2F2 ;}
Lithium tungstates such as LiWOF ₅ ;
_Lithium carboxylates _{such as HCO2Li , CH3CO2Li , CH2FCO2Li , CHF2CO2Li , CF3CO2Li , CF3CH2CO2Li , CF3CF2CO2Li , CF3CF2CF2CO2Li , CF3CF2CF2CF2CO2Li , and CF3CF2CF2CF2CF2CO2Li ;}
Lithium salts _{having an S═O group, such as FSO 3 Li, CH 3 SO 3 Li, CH 2 FSO 3 Li, CHF 2 SO 3 Li, CF 3 SO 3 Li, CF 3 CF 2 SO 3 Li , CF 3 CF 2 CF 2 SO 3 Li , CF 3 CF 2} CF ₂ CF 2 SO 3 Li, lithium methyl sulfate, lithium ethyl sulfate (C ₂ H ₅ OSO ₃ Li), and lithium 2,2,2-trifluoroethyl sulfate;
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 bisperfluoroethanesulfonylimide, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, lithium cyclic 1,2-ethanedisulfonylimide, lithium cyclic 1,3-propanedisulfonylimide, lithium cyclic 1,4-perfluorobutanedisulfonylimide, LiN(CF ₃ SO ₂ )(FSO ₂ ), LiN(CF ₃ SO ₂ )(C ₃ F ₇ SO ₂ ), LiN(CF ₃ SO ₂ )(C _Lithium imide salts such as Li( _POF2 ) ₂ , Li( _POF2 ) _2, etc.;
_Lithium methide salts such as LiC( _FSO2 ) ₃ , LiC( _CF3SO2 ) _{3 ,} LiC( _C2F5SO2 ) _{3 ;}
Other examples include salts 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) (e.g., LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (iso-C ₃ F ₇ ) ₃ , LiPF ₅ (iso-C ₃ F ₇ ), 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 Examples of the _lithium salt include fluorine-containing organic _{lithium salts such as C 2 F 5 , LiBF 3 C 3 F 7 , LiBF 2 (CF 3 ) 2 , LiBF 2 (C 2 F 5 ) 2 , LiBF 2 ( CF 3 SO 2 ) 2 and LiBF 2 ( C 2 F 5} SO 2 ) 2 , LiSCN, LiB(CN) ₄ , LiB(C ₆ H ₅ ) ₄ , Li ₂ (C ₂ O ₄ ), LiP(C ₂ O ₄ ) ₃ , and Li ₂ B ₁₂ F _b H _12-b (b is an integer of 0 to 3).

Among them, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiTaF ₆ , LiPO ₂ F ₂ , FSO ₃ Li, CF ₃ SO ₃ Li, iN(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-perfluoroethane disulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiC(FSO ₂ ) ₃ , LiC(CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , LiBF ₃ CF ₃ , LiBF ₃ C _2F5 , _LiPF3 ( _CF3 ) ₃ , _LiPF3 ( _C2F5 ) _{3 ,} etc. are preferred because they have the effect of improving output characteristics, high-rate charge/discharge characteristics, high-temperature storage characteristics, cycle characteristics _, etc., and at least one lithium salt selected from the group consisting of _LiPF6 , LiN( _FSO2 ) ₂ (lithium bis(fluorosulfonyl)imide (LIFSI)) and LiN( _CF3SO2 ) ₂ (lithium bis(trifluoromethanesulfonyl)imide (LITFSI)) is more preferred, and at least one lithium salt selected from _the group consisting of _LiPF6 , LiFSI and LiTFSI is particularly preferred.

These electrolyte salts may be used alone or in combination of two or more thereof. A preferred example of a combination of two _or more thereof is _a combination of _LiPF6 and _LiBF4 , or a combination of _LiPF6 and _LiPO2F2 , _C2H5OSO3Li or _{FSO3Li ,} which has the effect of improving high-temperature storage characteristics, load characteristics and cycle characteristics.

In this case, there is no limitation on the amount of LiBF ₄ , LiPO ₂ F ₂ , C ₂ H ₅ OSO ₃ Li or FSO ₃ Li mixed relative to 100% by mass of the entire electrolyte solution, and it is arbitrary as long as it does not significantly impair the effects of the present disclosure. However, it is usually 0.01% by mass or more, preferably 0.1% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, relative to the electrolyte solution.

Another example is the combined use of an inorganic lithium salt and an organic lithium salt, which has the effect of suppressing deterioration due to storage at high temperatures. Examples of organic lithium salts include CF ₃ SO ₃ Li, LiN(FSO ₂ ) ₂ (LIFSI), LiN(FSO ₂ )(CF ₃ SO ₂ ), LiN(CF ₃ SO ₂ ) ₂ (LITFSI), LiN(C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,2-perfluoroethane disulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiC(FSO ₂ ) ₃ , LiC(CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiPF ₃ (CF ₃ ) ₃ , and LiPF ₃ (C ₂ F ₅ ) _3, etc. In this case, the ratio of the organic lithium salt to 100% by mass of the entire electrolyte solution is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, and is preferably 30% by mass or less, particularly preferably 20% by mass or less.

The concentrations of these electrolyte salts in the electrolyte solution are not particularly limited as long as they do not impair the effects of the present disclosure. To maintain the electrical conductivity of the electrolyte solution in a favorable range and ensure good battery performance, the total molar concentration of lithium in the electrolyte solution is preferably 0.3 mol/L or more, more preferably 0.4 mol/L or more, even more preferably 0.5 mol/L or more, and particularly preferably 1.0 mol/L or more, and is preferably 3 mol/L or less, more preferably 2.5 mol/L or less, and even more preferably 2.0 mol/L or less.

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

As the ether compound, a chain ether having 2 to 10 carbon atoms and a cyclic ether having 3 to 6 carbon atoms are preferred.
Examples of chain ethers having 2 to 10 carbon atoms include dimethyl ether, diethyl ether, di-n-butyl ether, dimethoxymethane, methoxyethoxymethane, diethoxymethane, dimethoxyethane, methoxyethoxyethane, diethoxyethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol, diethylene glycol dimethyl ether, pentaethylene glycol, triethylene glycol dimethyl ether, triethylene glycol, tetraethylene glycol, tetraethylene glycol dimethyl ether, and diisopropyl ether.

Cyclic ethers having 3 to 6 carbon atoms include 1,2-dioxane, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, metaformaldehyde, 2-methyl-1,3-dioxolane, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-(trifluoroethyl)dioxolane 2,2-bis(trifluoromethyl)-1,3-dioxolane, and fluorinated compounds thereof. Among these, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, and crown ether are preferred because they have a high ability to solvate lithium ions and improve the degree of ionic dissociation. Dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferred because they have low viscosity and provide high ionic conductivity.

Furthermore, fluorinated ethers other than the fluorinated ether (E) can also be suitably used as the ether compound.

The compositions of the present disclosure may be prepared using the above-described components by any method.

The composition of the present disclosure can be suitably applied to, for example, electrochemical devices such as secondary batteries such as lithium ion secondary batteries, lithium ion capacitors, hybrid capacitors, electric double layer capacitors, etc. Hereinafter, a nonaqueous electrolyte battery using the composition of the present disclosure will be described.
The nonaqueous electrolyte battery can have a known structure and typically includes a positive electrode and a negative electrode capable of absorbing and desorbing ions (e.g., lithium ions) and the composition (electrolyte) of the present disclosure. An electrochemical device including such a composition (electrolyte) of the present disclosure also constitutes the present disclosure.

Examples of electrochemical devices include secondary batteries such as lithium ion secondary batteries, lithium ion capacitors, capacitors (hybrid capacitors and electric double layer capacitors), radical batteries, solar cells (particularly dye-sensitized solar cells), lithium ion primary batteries, fuel cells, various electrochemical sensors, electrochromic elements, electrochemical switching elements, aluminum electrolytic capacitors, and tantalum electrolytic capacitors, with secondary batteries such as lithium ion secondary batteries, lithium ion capacitors, and electric double layer capacitors being preferred.
The present disclosure also includes a module including the electrochemical device.

The present disclosure also relates to a secondary battery comprising the composition (electrolyte) of the present disclosure.
The secondary battery preferably comprises a positive electrode, a negative electrode, and the above-mentioned electrolyte solution.
The secondary battery is preferably a lithium ion secondary battery.

<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 is capable of electrochemically absorbing and releasing lithium ions, but examples include lithium-containing transition metal composite oxides, lithium-containing transition metal phosphate compounds, sulfur-based materials, and conductive polymers. Among these, lithium-containing transition metal composite oxides and lithium-containing transition metal phosphate compounds are preferred as positive electrode active materials, and lithium-containing transition metal composite oxides that generate high voltage are particularly preferred.

The transition metal of the lithium-containing transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc., and specific examples include lithium-cobalt composite oxides such as _LiCoO2 , lithium- _nickel composite oxides such as _LiNiO2 , lithium-manganese composite oxides such as LiMnO2, _LiMn2O4 , _{and Li2MnO4 ,} and lithium transition metal composite oxides in which some of the main transition metal atoms of these lithium transition metal composite oxides have been substituted with other elements such as Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, and W. _{Specific examples of the substituted compounds include LiNi0.5Mn0.5O2 , LiNi0.85Co0.10Al0.05O2 , LiNi0.5Co0.2Mn0.3O2 , LiNi0.6Co0.2Mn0.2O2 , LiNi0.33Co0.33Mn0.33O2 , LiNi0.8Co0.1Mn0.1O2 , LiNi0.45Co0.10Al0.45O2 , LiMn1.8Al0.2O4 , and LiMn1.5Ni0.5O . ​ ​ ​ ​ ​ ​ 4,} etc.

Among _these , the lithium _- containing transition metal composite oxides preferably include _{LiMn1.5Ni0.5O4} , _{LiNi0.5Co0.2Mn0.3O2} , _{and LiNi0.6Co0.2Mn0.2O2 ,} which have high energy density even at high voltages. Among these, _{LiMn1.5Ni0.5O4} is preferred for high _{voltages of 4.4 V} or _{higher .}

Among _these , _{LiNi0.6Co0.2Mn0.2O2} , _{LiNi0.8Co0.1Mn0.1O2} , _{and LiNi0.85Co0.10Al0.05O2 are preferred} as _the lithium-containing transition metal composite oxides, since they can provide _a high-capacity _{lithium ion} secondary _battery .

The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc., and specific examples include iron phosphates such as _LiFePO4 , _Li3Fe2 ( _PO4 ) ₃ , _{and LiFeP2O7} , cobalt phosphates such as _LiCoPO4 , and lithium transition metal phosphate compounds in _which part of the transition metal atoms that constitute the main components of these compounds have been substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si.

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

Among these, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is preferred because it allows provision of a lithium ion secondary battery with high energy density and high output.

_Other examples _{of the} positive _electrode active material include _{LiFePO4 , LiNi0.8Co0.2O2 , Li1.2Fe0.4Mn0.4O2 , LiNi0.5Mn0.5O2} , _{LiV3O6 , and Li2MnO3} .

The content of the positive electrode active material is preferably 50 to 99.5% by mass of the positive electrode mixture, and more preferably 80 to 99% by mass, in terms of high battery capacity. The content of the positive electrode active material in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 99% by mass or less, more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electrical 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.
Any material can be used as the binder as long as it is safe for the solvent and electrolyte used in producing the electrode. Examples of the binder include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, chitosan, alginic acid, polyacrylic acid, polyimide, cellulose, and nitrocellulose; rubber-like polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or hydrogenated products thereof; and EPDM (ethylene-propylene-diene rubber). Examples of suitable polymers include thermoplastic elastomeric polymers such as styrene-ethylene-butadiene-styrene terpolymers, styrene-isoprene-styrene block copolymers, and hydrogenated products thereof; soft resinous polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride copolymers, and tetrafluoroethylene-ethylene copolymers; and polymer compositions having ionic conductivity for alkali metal ions (particularly lithium ions). These may be used alone or in any combination and ratio of two or more.

The binder content, expressed as the proportion of binder in the positive electrode active material layer, is typically 0.1% by mass or more, preferably 1% by mass or more, and more preferably 1.2% by mass or more, and is typically 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, and most preferably 10% by mass or less. If the binder proportion is too low, the positive electrode active material may not be sufficiently held in place, resulting in insufficient mechanical strength of the positive electrode and possibly degrading battery performance such as cycle characteristics. On the other hand, if the binder proportion is too high, it may lead to a decrease in battery capacity and conductivity.

Any known conductive material can be used as the conductive material. Specific examples include metal materials such as copper, nickel, and gold; graphite (e.g., natural graphite and artificial graphite); carbon black (e.g., acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black); and carbon materials such as needle coke, carbon nanotubes, fullerenes, and amorphous carbon (e.g., VGCF). These materials may be used alone or in any combination and ratio of two or more. The conductive material is typically present in the positive electrode active material layer in an amount of at least 0.01% by mass, preferably at least 0.1% by mass, and more preferably at least 1% by mass, and typically at most 50% by mass, preferably at most 30% by mass, and more preferably at most 15% by mass. A content below this range may result in insufficient conductivity. Conversely, a content above this range may result in a decrease in battery capacity.

There are no particular restrictions on the type of solvent used to form the slurry, as long as it is capable of dissolving or dispersing the positive electrode active material, conductive material, binder, and thickener used as needed. Either an aqueous or organic solvent may be used. Examples of aqueous solvents include water and a mixture of alcohol and water. Examples of organic solvents 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); amides such as N-methylpyrrolidone (NMP), N-butylpyrrolidone (NBP), 3-methoxy-N,N-dimethylpropionamide, dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphalamide and dimethyl sulfoxide.

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

The shape of the current collector may be, for metal materials, metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punched metal, foam metal, etc.; for carbon materials, it may be carbon plate, carbon thin film, carbon cylinder, etc. Among these, metal thin film is preferred. The thin film may be formed into a mesh as appropriate. The thickness of the thin film is optional, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the thin film is thinner than this range, the strength required as a current collector may be insufficient. Conversely, if the thin film is thicker than this range, it may be difficult to handle.

It is also preferable to coat the surface of the current collector with a conductive additive, as this reduces the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of conductive additives include carbon and precious metals such as gold, platinum, and silver.

The positive electrode can be manufactured by a conventional method. For example, the positive electrode active material can be mixed with the binder, thickener, conductive material, solvent, etc., to form a slurry positive electrode mixture, which can then be applied to a current collector, dried, and pressed to increase density.

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

The negative electrode active material is not particularly limited as long as it is capable of electrochemically absorbing and releasing lithium ions. Specific examples include carbon materials, silicon materials, metal materials, and conductive polymers. These may be used alone or in any combination of two or more.

These carbon materials include natural graphite, artificial graphite, and graphite obtained by surface treating such graphite with pitch or other organic substances and then carbonizing it. These materials may be used alone or in any combination of two or more.

The silicon material may be silicon alone or a composite material containing silicon and one or more other constituent elements (cobalt, iron, magnesium, titanium, vanadium, chromium, manganese, nickel, copper, zinc, gallium, zirconium, boron, carbon, aluminum, phosphorus, etc.). These may be used alone or in any combination of two or more. From the viewpoint of obtaining excellent battery capacity, the silicon material is preferably SiO _v (0<v≦2), SnO _w (0≦w≦2), Si-Co-C composite material, or Si-Ni-C composite material.

The above silicon material is preferably used in combination with the above carbon material. In this case, the mass ratio of silicon material to carbon material is preferably 1-20:99-80.

Examples of the metal material include metal materials containing metallic elements such as lithium and tin. The metal material may be a simple metal, or a compound such as an alloy, oxide, carbide, nitride, silicide, sulfide, or phosphide. These may be used alone or in any combination of two or more. From the viewpoint of obtaining excellent battery capacity, metal materials containing lithium are preferred as the metal material, and lithium metal (simple lithium metal) is more preferred.

From the standpoint of high current density charge/discharge characteristics, lithium-containing metal materials are preferably materials containing lithium and titanium, and lithium and titanium composite oxides (hereinafter abbreviated as "lithium titanium composite oxides") are more preferred.

The lithium titanium composite oxide may be a compound represented by the general formula:
Li _x Ti _y M _z O ₄
[In the formula, M represents at least one element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb.]
It is preferable that the compound is a compound represented by the following formula:
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
The structure of is particularly preferred because it has a good balance of battery performance.

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

It is preferable that the above-mentioned negative electrode mixture further contains a binder, a thickener, and a conductive material.

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

In particular, when a rubber-like polymer such as SBR is contained as the main component, the ratio of the binder to the negative electrode active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, and more preferably 0.6% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. Furthermore, when a fluorine-based polymer such as polyvinylidene fluoride is contained as the main component, the ratio of the binder 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, and usually 15% by mass or less, preferably 10% by mass or less, and more preferably 8% by mass or less.

Conductive materials for the negative electrode include metal materials such as copper and nickel; and carbon materials such as graphite and carbon black.

The solvent for forming the slurry is not particularly limited in type as long as it is capable of dissolving or dispersing the negative electrode active material, the binder, and the thickener and conductive material used as needed, and either an aqueous solvent or an organic solvent may be used.
Examples of aqueous solvents include water and alcohol, and examples of organic solvents include N-methylpyrrolidone (NMP), N-butylpyrrolidone (NBP), 3-methoxy-N,N-dimethylpropionamide, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, and hexane.

Materials for the negative electrode current collector include copper, nickel, and stainless steel. Among these, copper foil is preferred because it is easy to process into a thin film and is cost-effective.

The negative electrode can be manufactured by a conventional method. For example, the negative electrode material can be prepared by adding the aforementioned binder, thickener, conductive material, solvent, etc. to form a slurry, which can then be applied to a current collector, dried, and pressed to achieve high density. Furthermore, when an alloy material is used, a thin film layer (negative electrode active material layer) containing the aforementioned negative electrode active material can also be formed by a method such as vapor deposition, sputtering, or plating.

<Separator>
The secondary battery of the present disclosure preferably further includes a separator.
The material and shape of the separator are not particularly limited as long as they are stable to the electrolyte solution and have excellent liquid retention properties, and any known separator can be used. Among them, it is preferable to use a material that is stable to the electrolyte solution, such as a resin, glass fiber, or inorganic material, and that is in the form of a porous sheet or nonwoven fabric, which has excellent liquid retention properties.

Resin and glass fiber separator materials that can be used include, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, and glass filters. These materials may be used alone or in any combination and ratio, such as polypropylene/polyethylene two-layer films and polypropylene/polyethylene/polypropylene three-layer films. Among these, porous sheets or nonwoven fabrics made from polyolefins such as polyethylene and polypropylene are preferred for the separator, as they have good electrolyte permeability and shutdown effect.

On the other hand, inorganic materials include, 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, and are used in particulate or fibrous form.

The separator may take the form of a thin film such as a nonwoven fabric, woven fabric, or microporous film. A thin film with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition to the above-mentioned independent thin film, a separator may be used in which a composite porous layer containing the above-mentioned inorganic particles is formed on the surface of the positive electrode and/or negative electrode using a resin binder. For example, a porous layer may be formed on both sides of the positive electrode using alumina particles with a 90% particle size of less than 1 μm and a fluororesin as a binder.

The secondary battery of the present disclosure may have any shape, including, for example, cylindrical, prismatic, laminated, coin, and large shapes. The shapes and configurations of the positive electrode, negative electrode, and separator can be modified according to the shape of each battery.

A module equipped with the secondary battery of the present disclosure is also part of the present disclosure.

The present disclosure also includes an electric double layer capacitor comprising the composition of the present disclosure.
The electric double layer capacitor may include a positive electrode, a negative electrode, and the above-mentioned electrolyte solution.
In the electric double layer capacitor, at least one of the positive electrode and the negative electrode is a polarizable electrode, and the following electrodes described in detail in Japanese Patent Laid-Open Publication No. 9-7896 can be used as the polarizable electrode and the non-polarizable electrode.

The composition of the present disclosure is useful as an electrolyte for large-scale lithium-ion secondary batteries for hybrid vehicles and distributed power sources, and for electric double-layer capacitors.

Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims.

The present disclosure will now be described using examples, but the present disclosure is not limited to these examples.

(Production and evaluation of lithium metal secondary batteries)
[Preparation of Electrolyte Solution]
The materials were mixed in the proportions shown in Table 1 to obtain a non-aqueous electrolyte solution.

[Preparation of Positive Electrode]
97% by mass of Li( _{Ni0.8Mn0.1Co0.1} ) _O2 ( _NMC811 ) as the positive _electrode active material, 1.5% by mass of acetylene black as the conductive material, and 1.5% by mass of polyvinylidene fluoride (PVdF) as the binder were mixed in N-methylpyrrolidone solvent to form a slurry. The resulting slurry was applied to a 15 μm thick aluminum foil current collector, dried, and then compression molded using a press. The electrode was cut into shapes with a width of 30 mm, a length of 30 mm, and an uncoated portion of 4 mm wide and 5 mm long to form a positive electrode.

[Fabrication of negative electrode]
A 0.15 mm thick lithium foil was cut into a width of 32 mm and a length of 32 mm as the negative electrode active material, and then rolled with a PTFE roll onto a copper mesh having terminal portions of 33 mm wide, 33 mm long, and 4 mm wide, 5 mm long to form a negative electrode.

[Preparation of Laminated Cell]
The positive and negative electrodes prepared as described above were stacked on a polypropylene separator in the order of negative electrode, separator, and positive electrode to prepare a battery element. This battery element was inserted into a bag made of a laminate film of an aluminum sheet (40 μm thick) coated on both sides with a resin layer, with the positive and negative electrode terminals protruding, and the electrolyte solutions of the Examples and Comparative Examples shown in Table 1 were then poured into the bag, which was then vacuum-sealed to prepare a pouch-type lithium metal secondary battery.

[Cycle test]
The laminated cell produced above was subjected to constant current-constant voltage charging (hereinafter referred to as CC/CV charging) at 25°C to 4.15 V at a current equivalent to 0.2 C (0.05 C cut), and then discharged to 3.0 V at a constant current of 0.2 C. This constituted one cycle, and 5 cycles of formation cycles were performed. Thereafter, 200 cycles of 0.5 C constant current-constant voltage charging and constant current discharging (between 4.15 and 3.0 V) were performed in a thermostatic bath at 40°C.
The ratio of the discharge capacity at the 200th cycle to the discharge capacity at the first cycle at 40° C. was determined and defined as the cycle capacity retention rate (%).
(Discharge capacity after 200 cycles)/(Discharge capacity at first cycle)×100=Cycle capacity retention rate (%)

[Evaluation of gas generation amount]
The volume of the battery before and after the cycle test was measured by Archimedes' method, and the amount of gas generated was calculated from the change in volume before and after the cycle.
(Battery volume after cycle test) - (Battery volume before cycle test) = Amount of gas generated (ml)

(Production and evaluation of lithium-ion secondary batteries)
[Preparation of Electrolyte Solution]
The materials were mixed in the proportions shown in Table 2 to obtain non-aqueous electrolyte solutions.

[Preparation of Positive Electrode]
_A positive electrode _mixture slurry was prepared by mixing _{LiNi0.5Mn1.5O4} as the positive electrode active material, acetylene black as the conductive material, and an N-methyl-2-pyrrolidone dispersion of polyvinylidene fluoride (PVdF) as the binder in a solids ratio of 92/3/5 (mass % ratio) of the active material, conductive material, and binder. The resulting positive electrode mixture slurry was uniformly applied to a 15 μm thick aluminum foil current collector, dried, and then compression-molded using a press to form a positive electrode.

[Fabrication of negative electrode]
As the negative electrode active material, artificial graphite powder, SiO powder, an aqueous dispersion of carboxymethyl cellulose sodium as a thickener (concentration of carboxymethyl cellulose sodium 1% by mass), and an aqueous dispersion of styrene-butadiene rubber as a binder (concentration of styrene-butadiene rubber 50% by mass) were used, and the solid content ratio of the artificial graphite powder, SiO powder, thickener, and binder was 82.45/14.55/1.5/1.5 (mass%) in an aqueous solvent to prepare a negative electrode mixture slurry. The mixture was uniformly applied to a 10 μm thick copper foil, dried, and then compressed using a press to form a negative electrode.

[Preparation of Laminated Cell]
The positive and negative electrodes prepared as described above and a polypropylene separator were stacked in this order to prepare a battery element. This battery element was inserted into a bag made of a laminate film in which both sides of an aluminum sheet (40 μm thick) were coated with a resin layer, with the positive and negative terminals protruding. The electrolyte solutions of the Examples and Comparative Examples shown in Table 2 were then poured into the bag, which was then vacuum-sealed to prepare a pouch-type lithium-ion secondary battery.

[Cycle test]
The laminated cell produced above was subjected to CC/CV charging (0.05 C cut) at 25°C to 4.9 V at a current equivalent to 0.1 C, and then discharged to 3.0 V at a constant current of 0.1 C. This constituted one cycle, and 5 cycles of formation cycles were performed. Thereafter, 200 cycles of 0.5 C constant current-constant voltage charging and constant current discharging (between 4.9 and 3.0 V) were performed in a thermostatic bath at 40°C.
The ratio of the discharge capacity at the 200th cycle to the discharge capacity at the first cycle at 40° C. was determined and defined as the cycle capacity retention rate (%).
(Discharge capacity after 200 cycles)/(Discharge capacity at first cycle)×100=Cycle capacity retention rate (%)

[Evaluation of gas generation amount]
The volume of the battery before and after the cycle test was measured by Archimedes' method, and the amount of gas generated was calculated from the change in volume before and after the cycle.
(Battery volume after cycle test) - (Battery volume before cycle test) = Amount of gas generated (ml)

The abbreviations in the table are as follows:
<Compound (A)>
A-1: HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OH
A-2: HCF ₂ -CF ₂ -CH ₂ -O-CH ₂ -CH ₂ -OH
A-3: HCF ₂ -CH ₂ -O-CH ₂ -CH ₂ -OH
A-4: CF ₃ -CF ₂ -CH ₂ -O-CH ₂ -CH ₂ -OH
A-5: CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -OH
A-6: HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OLi
A-7: HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OK
A-8: HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -ONa
A-9: HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OCs
A-10: CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -OLi
<Fluorinated Ether (E)>
E-1: HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H
E-2: HCF ₂ -CF ₂ -CH ₂ -O-CH ₂ -CH ₂ -CH ₂ -CF ₂ -CF ₂ H
E-3: HCF ₂ -CH ₂ -O-CH ₂ -CH ₂ -O-CH ₂ -CF ₂ H
E-4: CF ₃ -CF ₂ -CH ₂ -O-CH ₂ -CH ₂ -O-CH ₂ -CF ₂ -CF ₃
E-5: CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃
E-6: HCF ₂ -CF ₂ -CH ₂ -O-CF ₂ -CF ₂ H
<Other solvent components>
DME: _CH3 -O- _CH2 - _CH2 -O- _CH3
EC: ethylene carbonate DMC: dimethyl carbonate FEC: fluoroethylene carbonate TFMEC: trifluoromethylethylene carbonate TFEMC: CF ₃ —CH ₂ —COO—CH ₃ (trifluoroethylmethyl carbonate)
<Lithium salt>
LiFSI: Lithium bis(fluorosulfonyl)imide LiTFSI: Lithium bis(trifluoromethanesulfonyl)imide LiPF ₆ : Lithium hexafluorophosphate

Claims (19)

An electrolyte composition comprising a compound (A) represented by the following formula (A):
(A) Rf ¹ -O-CH ₂ -CH ₂ -O-R ¹
(In the formula, ^Rf1 is a fluoroalkyl group having 1 to 6 carbon atoms, and ^R1 is H, Li, Na, K, or Cs.) The Rf ¹ is
HCF ₂ -CF ₂ -,
HCF ₂ -CF ₂ -CH ₂ -,
HCF ₂ -CH ₂ -,
CF ₃ —CF ₂ —CH ₂ —, or
2. The electrolyte composition according to claim 1, which is CF ₃ --CHF--CF ₂ --. 3. The electrolyte composition according to claim ¹ , wherein R1 is H or Li. The electrolyte solution composition according to any one of claims 1 to 3, wherein the content of compound (A) is 0.0001 to 30,000 ppm relative to the electrolyte solution composition. The compound (A) is
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OH,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OLi,
CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OH, and
5. The electrolyte composition according to claim 1, which is at least one selected from the group consisting of CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OLi. 6. The composition for an electrolyte solution according to claim 1, which contains a fluorinated ether (E) represented by the following formula (E):
(E) Rf ² -O-R ²
(In the formula, ^Rf2 is a fluoroalkyl group having 1 to 5 carbon atoms, and ^R2 is H or an alkyl group having 1 to 6 carbon atoms. The alkyl group of ^R2 may have an ether bond and/or fluorine.) 7. The electrolyte composition according to claim 6, wherein Rf ² is HCF ₂ —CF ₂ —. The ^R2 is
—CH ₂ —CH ₂ —O—CF ₂ —CF ₂ H, or
-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃
8. The composition for an electrolyte solution according to claim 6 or 7, wherein The fluorinated ether (E) is
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H, and
CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃
The composition for an electrolyte solution according to any one of claims 6 to 8, which is at least one selected from the group consisting of: The electrolyte solution composition according to any one of claims 6 to 9, wherein the content of the fluorinated ether (E) is 0.01 to 99 mass% of the electrolyte solution composition. 11. The composition for an electrolyte solution according to claim 1, which contains at least one lithium salt selected from the group consisting of LiPF ₆ , LiFSI, and LiTFSI. The compound (A) is
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OH,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OLi,
CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OH, and
at least one selected from the group consisting of CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OLi;
the content of the compound (A) is 0.003 to 30,000 ppm relative to the electrolyte solution composition;
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H, and
CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃
At least one fluorinated ether (E) selected from the group consisting of:
12. The composition for an electrolyte solution according to claim 1, wherein the content of the fluorinated ether (E) is 0.5 to 50 mass % based on the mass of the composition for an electrolyte solution. A secondary battery comprising the electrolyte composition according to claim 12 and lithium metal as a negative electrode active material. Compound (A) is
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OH,
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -OLi,
CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OH, and
at least one selected from the group consisting of CF ₃ —CHF—CF ₂ —O—CH ₂ —CH ₂ —OLi;
the content of the compound (A) is 0.01 to 30,000 ppm relative to the electrolyte solution composition;
HCF ₂ -CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CF ₂ H, and
CF ₃ -CHF-CF ₂ -O-CH ₂ -CH ₂ -O-CF ₂ -CHF-CF ₃
At least one fluorinated ether (E) selected from the group consisting of:
12. The composition for an electrolyte solution according to claim 1, wherein the content of the fluorinated ether (E) is 40 to 95 mass % based on the mass of the composition for an electrolyte solution. A secondary battery comprising the electrolyte composition according to claim 14 and a silicon material as a negative electrode active material. The electrolyte composition according to any one of claims 1 to 12 and 14, which is for use in a secondary battery. An electrochemical device comprising the electrolyte composition according to any one of claims 1 to 12 and 14. A secondary battery comprising the electrolyte composition according to any one of claims 1 to 12 and 14. A lithium ion secondary battery comprising the composition for an electrolyte solution according to any one of claims 1 to 12 and 14.