JP2013122931A - Overcharge inhibitor, nonaqueous electrolytic solution, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery that contains an overcharge inhibitor capable of inhibiting rapid heat generation and ignition caused by overcharging.SOLUTION: An overcharge inhibitor contains a compound represented by the formula (1), and/or a compound represented by the formula (2).

Description

The present invention relates to an overcharge inhibitor, a non-aqueous electrolyte using the overcharge inhibitor, and a lithium ion secondary battery.

The required characteristics for non-aqueous electrolytes for lithium ion secondary batteries are becoming stricter year by year. As one of such required characteristics, it is required to solve the problem of ensuring safety during overcharging (for example, nonflammability and destruction resistance).

As a solution to this problem, it is known to add a compound such as biphenyl, cyclohexylbenzene, toluene, or a t-alkylbenzene derivative to the non-aqueous electrolyte as an overcharge inhibitor (Patent Documents 1 to 12).

In particular, Patent Document 13 discloses a fluorinated aromatic compound in which part or all of the hydrogen atoms of benzene, toluene, xylene, anisole or biphenyl are substituted with fluorine atoms, such as monofluorobenzene, difluorobenzene, perfluorobenzene, It is described that trifluoromethylbenzene, difluorotoluene, difluoroanisole or fluorobiphenyl is excellent in oxidation resistance and effective in preventing overcharge.

On the other hand, in order to improve nonflammability (flame retardancy) without degrading the performance as a non-aqueous electrolyte, it has also been proposed to add a fluorinated solvent (Patent Documents 14 to 24).

International Publication No. 2005/048391 Pamphlet JP 2004-311442 A JP 2005-267966 A International Publication No. 2005/074067 Pamphlet JP 2003-77478 A JP 2004-63114 A JP 2003-132950 A JP 2004-134261 A JP 2005-142157 A JP 2005-259680 A Japanese Patent Application Laid-Open No. 08-037044 International Publication No. 2002/029922 Pamphlet International Publication No. 2010/013739 Pamphlet JP 09-097627 A Japanese Patent Laid-Open No. 11-026015 JP 2000-294281 A JP 2001-052737 A Japanese Patent Laid-Open No. 11-307123 JP-A-10-112334 International Publication No. 2006/088009 Pamphlet International Publication No. 2006/106655 Pamphlet International Publication No. 2006/106656 Pamphlet International Publication No. 2006/106657 Pamphlet International Publication No. 2008/007734 Pamphlet

However, the conventional overcharge preventing agent sometimes deteriorates the cycle characteristics of the lithium ion secondary battery.
With the recent reduction in weight and size of electrical products, development of lithium ion secondary batteries and the like having high energy density has been promoted. In particular, in the future, when lithium ion secondary batteries are applied to vehicles, safety and battery characteristics will become increasingly important.

The present invention provides an overcharge inhibitor capable of suppressing rapid heat generation and ignition during overcharge without impairing cycle characteristics, a non-aqueous electrolyte using the overcharge inhibitor, and a lithium ion secondary An object is to provide a battery.

The present invention relates to formula (1):

(In the formula, R ^{1 to} R ¹⁰ are the same or different, and all are —H, —CH ₃ , —OR ¹¹ , —R ¹² —O—R ¹³ , or —O—R ¹² —O—R ^13. R ¹¹ is an alkyl group having 1 to 6 carbon atoms or a fluorine-containing alkyl group, R ¹² is an alkylene group having 1 to 3 carbon atoms, and R ¹³ is an alkyl group having 1 to 4 carbon atoms or fluorine-containing An alkyl group) and / or formula (2):

(Wherein, R ¹⁴ and R ¹⁵ are the same or different, and both are alkyl groups having 1 to 6 carbon atoms).

In the compound represented by the above formula (1), 1 to ^{3 of} R ¹ , R ² , R ³ , R ⁴ and R ⁵ , and R ⁶ , R ⁷ , R ⁸ , R ⁹ and R ¹⁰ 1 to 3 of them are the same or different, and all are —CH ₃ , —OR ¹¹ , —R ¹² —O—R ¹³ , or —O—R ¹² —O—R ¹³ , and R ¹¹ is carbon. an alkyl group having 1 to ^{6, R 12} is an alkylene group having 1 to 3 carbon ^{atoms, R 13} is preferably an alkyl group having 1 to 4 carbon atoms.
Furthermore, in the compound represented by the above formula (1), 1 to ^{3 of} R ¹ , R ² , R ³ , R ⁴ and R ⁵ , and R ⁶ , R ⁷ , R ⁸ , R ⁹ and R 1-3 of ^10, the same or different and each is _-CH 3, ^{-OR 11,} or ^{a -O-R 12 -O-R 13} , R 11 is an alkyl group having 1 to 4 carbon atoms More preferably, R ¹² is an alkylene group having 1 to 3 carbon atoms, and R ¹³ is an alkyl group having 1 to 4 carbon atoms.
In the compound represented by the above formula (2), R ¹⁴ and R ¹⁵ are the same or different, and each is preferably an alkyl group having 1 to 4 carbon atoms.

The present invention is also a non-aqueous electrolyte characterized by including the above-described overcharge inhibitor, a non-aqueous solvent, and an electrolyte salt.
The present invention is also a lithium ion secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte described above.
The present invention also provides formula (1):

(In the formula, R ^{1 to} R ¹⁰ are the same or different, and all are —H, —CH ₃ , —OR ¹¹ , —R ¹² —O—R ¹³ , or —O—R ¹² —O—R ^13. R ¹¹ is an alkyl group having 1 to 6 carbon atoms or a fluorine-containing alkyl group, R ¹² is an alkylene group having 1 to 3 carbon atoms, and R ¹³ is an alkyl group having 1 to 4 carbon atoms or fluorine-containing An alkyl group) and / or formula (2):

(Wherein R ¹⁴ and R ¹⁵ are the same or different, and each is an alkyl group having 1 to 6 carbon atoms), a step of preparing a non-aqueous electrolyte, and the above non-aqueous electrolyte And a step of charging the lithium ion secondary battery, and a method for suppressing heat generation during overcharging of the lithium ion secondary battery.
The present invention is described in detail below.

According to the present invention, the compound of the formula (1) and / or the compound of the formula (2) does not react specifically even at high temperatures due to overcharge, and exhibits an excellent overcharge prevention effect. Further, the cycle characteristics are not impaired. For this reason, the non-aqueous electrolyte containing the overcharge inhibitor of the present invention can provide a lithium ion secondary battery having excellent cycle characteristics and high safety.

2 is a schematic assembly perspective view of a laminate cell manufactured in Test 1. FIG. 3 is a schematic plan view of a laminate cell produced in Test 1. FIG.

The overcharge inhibitor of the present invention is
Formula (1):

(In the formula, R ^{1 to} R ¹⁰ are the same or different, and all are —H, —CH ₃ , —OR ¹¹ , —R ¹² —O—R ¹³ , or —O—R ¹² —O—R ^13. R ¹¹ is an alkyl group having 1 to 6 carbon atoms or a fluorine-containing alkyl group, R ¹² is an alkylene group having 1 to 3 carbon atoms, and R ¹³ is an alkyl group having 1 to 4 carbon atoms or fluorine-containing An alkyl group) and / or formula (2):

(Wherein, R ¹⁴ and R ¹⁵ are the same or different and both are alkyl groups having 1 to 6 carbon atoms).
For this reason, the secondary battery using the overcharge inhibitor of the present invention is capable of preventing sudden heat generation and ignition during overcharge without impairing cycle characteristics, and is excellent in safety. be able to.

In the compound represented by the formula (1), R ^{1 to} R ¹⁰ are the same or different, and all are —H, —CH ₃ , —OR ¹¹ , —R ¹² —O—R ¹³ , or —O—. R ¹² —O—R ¹³ , R ¹¹ is an alkyl group having 1 to 6 carbon atoms or a fluorine-containing alkyl group, R ¹² is an alkylene group having 1 to 3 carbon atoms, and R ¹³ is 1 to 3 carbon atoms. 4 alkyl groups or fluorine-containing alkyl groups.
The fluorine-containing alkyl group is a group in which part or all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms.

Among them, excellent cycle characteristics, and in that the secondary battery capable of suppressing the rapid heat generation or ignition during overcharge can be obtained, the compound of formula (1) is that wherein, R ^{1, R 2,} R ³ , R ⁴ and R ⁵ , and 1 to 3 of R ⁶ , R ⁷ , R ⁸ , R ⁹ and R ¹⁰ are the same or different, and both are —CH ₃ , —OR ¹¹ , —R ¹² —O—R ¹³ , or —O—R ¹² —O—R ¹³ , R ¹¹ is an alkyl group having 1 to 6 carbon atoms, and R ¹² is an alkylene having 1 to 3 carbon atoms. R ¹³ is preferably an alkyl group having 1 to 4 carbon atoms.

Further, the compound of formula (1) is represented by the formula: ^{1 to 3 of} R ¹ , R ² , R ³ , R ⁴ and R ⁵ , and R ⁶ , R ⁷ , R ⁸ , R ⁹ and R ¹⁰ . 1 to 3 of them are the same or different, and all are —CH ₃ , —OR ¹¹ , or —O—R ¹² —O—R ¹³ , and R ¹¹ is an alkyl group having 1 to 4 carbon atoms. More preferably, R ¹² is an alkylene group having 1 to 3 carbon atoms, and R ¹³ is an alkyl group having 1 to 4 carbon atoms.

Specifically as a compound of Formula (1), the compound represented by the following chemical formula is mentioned, for example.

Among these, the following compounds are preferable in that high cycle characteristics can be maintained.

The compound of formula (1) can be synthesized by the following method.
It can be synthesized by reacting an aromatic ring compound as a precursor with hexafluoroketone with an acid catalyst. Moreover, after making phenol and benzyl alcohol react with hexafluoroketone, it can synthesize | combine by making alcohol react with an alkyl halide and a vinyl compound.
Moreover, you may use a commercial item as a compound of Formula (1).

In the compound of formula (2), R ¹⁴ and R ¹⁵ are alkyl groups having 1 to 6 carbon atoms.
The number of carbon atoms is preferably 1 to 4 in that a secondary battery having excellent cycle characteristics and suppressing heat generation during overcharge can be obtained.
R ¹⁴ and R ¹⁵ may be the same or different, but are preferably the same from the viewpoint of easy synthesis.

As a compound of Formula (2), the following compounds are preferable at the point which can provide high cycling characteristics.

The compound of formula (2) can be synthesized, for example, by the following method.
The aromatic ring and hexafluoroketone are reacted under an acid catalyst. At this time, an alcohol form can be synthesized by increasing the amount of hexafluoroketone. It can be synthesized by reacting the alcohol with an alkyl halide or vinyl compound.

The overcharge inhibitor of the present invention is composed of the compound of formula (1) and / or the compound of formula (2) described above, but may further contain other conventional overcharge inhibitors.
Examples of conventional overcharge inhibitors include cyclohexylbenzene, biphenyl, triamylbenzene, fluorobenzene, perfluorobenzene, and the like.
When a conventional overcharge inhibitor is used in combination, the type and content thereof may be appropriately adjusted appropriately without affecting the effects of the present invention, particularly the overcharge prevention effect, but the content is generally It is preferable that it is 0.01-3 mass%.

By using such an overcharge inhibitor of the present invention, it is possible to prevent a sudden heat generation and ignition during overcharge while maintaining high cycle characteristics, and to obtain a secondary battery excellent in safety. it can. Such an overcharge inhibitor of the present invention can be suitably applied to, for example, a lithium ion secondary battery.
When the overcharge inhibitor of the present invention is applied to a secondary battery, a non-aqueous electrolyte containing the overcharge inhibitor of the present invention is prepared, and a secondary battery is manufactured using the nonaqueous electrolyte.

Hereinafter, the nonaqueous electrolytic solution using the overcharge inhibitor of the present invention will be described in detail.
Such a non-aqueous electrolyte is also one aspect of the present invention.

The nonaqueous electrolytic solution of the present invention comprises an overcharge inhibitor (I) comprising a compound represented by the formula (1) and / or a compound represented by the formula (2), a nonaqueous solvent (II), and And electrolyte salt (III).

The overcharge inhibitor (I) comprising the compound represented by the formula (1) and / or the compound represented by the formula (2) is the above-described overcharge inhibitor of the present invention.
Since such an overcharge inhibitor is included, the use of the non-aqueous electrolyte of the present invention produces a highly safe secondary battery that has excellent cycle characteristics and suppresses heat generation during overcharge. be able to.

The content of the overcharge inhibitor (I) is preferably 0.1 to 6% by mass in the non-aqueous electrolyte. If the content of the overcharge inhibitor (I) is too small, the overcharge prevention ability may be lowered, and if it is too much, the battery characteristics may be deteriorated. The content of the overcharge inhibitor (I) is more preferably 0.2% by mass or more, and more preferably 5% by mass or less.

Examples of the non-aqueous solvent (II) include fluorinated solvents and non-fluorinated solvents. By containing a fluorinated solvent, it is possible to obtain an effect of making the electrolyte solution flame-retardant, an effect of improving the low temperature characteristics, an improvement of rate characteristics, and an improvement of oxidation resistance.
Examples of the fluorine-based solvent include fluorine-containing ethers, fluorine-containing esters, fluorine-containing chain carbonates, and fluorine-containing cyclic carbonates.

Examples of the fluorine-containing ether include, for example, JP-A No. 08-037044, JP-A No. 09-097627, JP-A No. 11-026015, JP-A No. 2000-294281, JP-A No. 2001-052737, and the like. Examples thereof include compounds described in Kaihei 11-307123.

Among them, the formula (IIA) is preferable in that it has an appropriate boiling point and good compatibility with other solvents.
Rf ¹ ORf ² (IIA)
(Wherein Rf ¹ is a fluorine-containing alkyl group having 3 to 6 carbon atoms, and Rf ² is a fluorine-containing alkyl group having 2 to 6 carbon atoms).

Examples of Rf ¹ include HCF ₂ CF ₂ CH ₂ —, HCF ₂ CF ₂ CF ₂ CH ₂ —, HCF ₂ CF ₂ CF ₂ CF ₂ CH ₂ —, CF ₃ CF ₂ CH ₂ —, CF ₃ CFHCF ₂ CH Examples thereof include fluorine-containing alkyl groups having 3 to 6 carbon atoms such as _2- , HCF ₂ CF (CF ₃ ) CH ₂ —, and CF ₃ CF ₂ CH ₂ CH ₂ —.
Examples of Rf ² include —CF ₂ CF ₂ H, —CF ₂ CFHCF ₃ , —CF ₂ CF ₂ CF ₂ H, —CH ₂ CH ₂ CF ₃ , —CH ₂ CFHCF ₃ , —CH ₂ CH ₂ CF _2. Examples thereof include fluorine-containing alkyl groups having 2 to 6 carbon atoms such as CF ₃ .
Among them, Rf ¹ is a fluorine-containing alkyl group having 3 to 4 carbon atoms, Rf ² is that a fluorine-containing alkyl group having 2 to 3 carbon atoms, particularly preferably from ionic conductivity viewpoint of satisfactory.

Specific examples of the fluorine-containing ether represented by the formula (IIA) 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 , HCF ₂ CF ₂ CH ₂ OCH ₂ CFHCF ₃ , CF ₃ CF ₂ CH ₂ OCH ₂ CFHCF _{3 and the} like.
Among them, 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 are preferable in terms of compatibility with other solvents and good rate characteristics. CFHCF ₃ and CF ₃ CF ₂ CH ₂ OCF ₂ CFHCF ₃ are preferred.

Examples of the fluorine-containing ester include formula (IIB):
Rf ³ COORf ⁴ (IIB)
(In the formula, Rf ³ is an alkyl group having 1 to 2 carbon atoms or a fluorine-containing alkyl group, Rf ⁴ is an alkyl group having 1 to 4 carbon atoms or a fluorine-containing alkyl group, and Rf ³ and Rf ⁴ are Among them, a fluorine-containing ester represented by the formula (1) is preferably a fluorine-containing alkyl group from the viewpoint of high flame retardancy and good compatibility with other solvents.

The Rf ^3, specifically, for _{example, HCF 2 -, CF 3 -} , CF 3 CF 2 -, HCF 2 CF 2 -, CH 3 CF 2 -, CF 3 CH 2 -, CH 3 -, CH 3 CH _2- , and the like. Of these, CF ₃ -and HCF ₂ -are preferable from the viewpoint of good rate characteristics.

The Rf ^4, specifically, for _{example, -CF 3, -CF 2 CF 3} , -CH 2 CF 3, -CH 2 CH 2 CF 3, -CH (CF 3) 2, -CH 2 CF 2 CFHCF _{3, -CH 2 C 2 F 5} , -CH 2 CF 2 CF 2 H, -CH 2 CH 2 C 2 F 5, -CH 2 CF 2 CF 3, fluorine, such as _-CH 2 _CF 2 CF 2 CF ₃ An alkyl group; an alkyl group such as —CH ₃ , —C ₂ H ₅ , —C ₃ H ₇ , —CH (CH ₃ ) CH ₃ ;
Among them, —CH ₂ CF ₃ , —CH ₂ C ₂ F ₅ , —CH (CF ₃ ) ₂ , —CH ₂ CF ₂ CF ₂ H, —CH ₃ , -C ₂ H ₅ are preferred.

Specific examples of the fluorine-containing ester represented by the formula (IIB) include the following <1> to <3>.
<1> Rf ³ and Rf ⁴ are fluorine-containing alkyl groups:
CF ₃ C (═O) OCH ₂ CF ₃ , CF ₃ C (═O) OCH ₂ CF ₂ CF ₃ , CF ₃ C (═O) OCH ₂ CF ₂ CF ₂ H, HCF ₂ C (═O) OCH ₂ CF ₃ , HCF ₂ C (═O) OCH ₂ CF ₂ CF ₃ , HCF ₂ C (═O) OCF ₂ CF ₂ H
<2> Rf ³ is a fluorine-containing alkyl group:
CF ₃ C (═O) OCH ₃ , CF ₃ C (═O) OCH ₂ CH ₃ , HCF ₂ C (═O) OCH ₃ , HCF ₂ C (═O) OCH ₂ CH ₃ , CH ₃ CF ₂ C ( _{= O) OCH 3, CH 3} CF 2 C (= O) OCH 2 CH 3, CF 3 CF 2 C (= O) OCH 3, CF 3 CF 2 C (= O) OCH 2 CH 3
<3> Rf ⁴ is a fluorine-containing alkyl group:
_{CH 3 C (= O) OCH} 2 CF 3, CH 3 C (= O) OCH 2 CF 2 CF 3, CH 3 C (= O) OCH 2 CF 2 CF 2 H, CH 3 CH 2 C (= O) OCH ₂ CF ₃ , CH ₃ CH ₂ C (═O) OCH ₂ CF ₂ CF ₃ , CH ₃ CH ₂ C (═O) OCH ₂ CF ₂ CF ₂ H

Among these, <2> those in which Rf ³ is a fluorine-containing alkyl group and those in which <3> Rf ⁴ is a fluorine-containing alkyl group are preferable, since compatibility with other solvents and rate characteristics are good. CF ₃ C (═O) OCH ₃ , CF ₃ C (═O) OCH ₂ CH ₃ , HCF ₂ C (═O) OCH ₃ , HCF ₂ C (═O) OCH ₂ CH ₃ , CH ₃ C (═O _{) OCH 2 CF 3, CH 3} C (= O) OCH 2 CF 2 CF 3 are more preferred.

As the fluorine-containing chain carbonate, the formula (IIC):
Rf ⁵ OCOORf ⁶ (IIC)
(Wherein Rf ⁵ is a fluorine-containing alkyl group having 1 to 4 carbon atoms, and Rf ⁶ is an alkyl group having 1 to 4 carbon atoms or a fluorine-containing alkyl group). Is preferable from the viewpoint of high and rate characteristics.

The Rf ^5, for _{example, CF 3 -, C 2 F} 5 -, (CF 3) 2 CH-, CF 3 CH 2 -, C 2 F 5 CH 2 -, HCF 2 CF 2 CH 2 -, CF 2 CFHCF ₂ CH ₂ — and the like can be mentioned.
Examples of Rf ⁶ include CF ₃ −, C ₂ F ₅ —, (CF ₃ ) ₂ CH—, CF ₃ CH ₂ —, C ₂ F ₅ CH ₂ —, HCF ₂ CF ₂ CH ₂ —, and CF ₂ CFHCF. Examples thereof include a fluorine-containing alkyl group such as ₂ CH ₂ — or an alkyl group such as —CH ₃ , —C ₂ H ₅ , —C ₃ H ₇ , —CH (CH ₃ ) CH ₃ .
Among these, Rf ⁵ is preferably CF ₃ CH ₂ —, C ₂ F ₅ CH ₂ —, and Rf ⁶ is suitable in terms of appropriate viscosity, good compatibility with other solvents, and good rate characteristics. CF ₃ CH ₂ —, C ₂ F ₅ CH ₂ —, —CH ₃ , —C ₂ H ₅ are preferred.

Specific examples of the fluorine-containing chain carbonate represented by the formula (IIC) include, for example, CF ₃ CH ₂ OCOOCH ₂ CF ₃ , CF ₃ CF ₂ CH ₂ OCOOCH ₂ CF ₂ CF ₃ , CF ₃ CF ₂ CH ₂ OCOOCH ₃ , fluorinated chain carbonates such as CF ₃ CH ₂ OCOOCH ₃ and CF ₃ CH ₂ OCOOCH ₂ CH ₃ .
Among them, CF ₃ CH ₂ OCOOCH ₂ CF ₃ , CF ₃ CF ₂ CH ₂ OCOOCH ₂ CF ₂ CF ₃ , CF ₃ CH ₂ OCOOCH ₃ , CF ₃ CH ₂ OCOOCH ₂ CH ₃ is suitable for viscosity and flame retardancy In view of good compatibility with other solvents and rate characteristics, it is particularly preferable.
Further, for example, compounds described in JP-A-06-21992, JP-A-2000-327634, JP-A-2001-256983 and the like can also be exemplified.

As the fluorine-containing cyclic carbonate, the formula (IID):

(Wherein X ¹ , X ² , X ³ and X ⁴ are the same or different, and all are —H, —F, —CF ₃ , —CHF ₂ , —CH ₂ F, —OCH ₂ C ₂ F ₅ , — _{OCH 2 CF 2 CHF 2, -CF} (CF 3) 2, a _-C 2 _{F 5} or _-CH 2 CF _3, provided ^that, X ^1, X 2, at least one -F of ^{X 3} and ^{X 4,} A fluorine-containing cyclic carbonate represented by —CF ₃ , —OCH ₂ C ₂ F ₅ , —OCH ₂ CF ₂ CHF ₂ , —CF (CF ₃ ) ₂ , —C ₂ F ₅ or —CH ₂ CF ₃ ). However, it is preferable because of its large capacitance and high withstand voltage.

Specific examples of the fluorine-containing cyclic carbonate include the following compounds.

Of these, the following compounds are preferred.

In addition, as the non-aqueous solvent (II) for the lithium ion secondary battery, a known fluorine-based solvent may be used in combination.

The content of the fluorinated solvent is preferably 10 to 90% by volume in the non-aqueous solvent.
When the content of the fluorinated solvent is within the above range, an electrolyte solution excellent in flame retardancy, low temperature characteristics, rate characteristics, and oxidation resistance can be obtained.
The content is more preferably 20% by volume or more, more preferably 30% by volume or more, more preferably 60% by volume or less, still more preferably 50% by volume or less, and 45% by volume or less because safety is particularly improved. Is particularly preferred.

Examples of the non-fluorinated solvent include non-fluorinated cyclic carbonate, non-fluorinated chain carbonate, ester, lactone, sulfone, sulfolane and the like.
Of these, non-fluorinated cyclic carbonates and non-fluorinated chain carbonates are preferred from the viewpoint of good low-temperature characteristics and cycle characteristics.

Examples of the non-fluorinated cyclic carbonate include ethylene carbonate (EC), vinylene carbonate (VC), propylene carbonate (PC), butylene carbonate, vinyl ethylene carbonate, and the like.
Among them, it is selected from the group consisting of ethylene carbonate (EC), vinylene carbonate (VC), propylene carbonate (PC), and butylene carbonate because it has a high dielectric constant and is excellent in solubility and rate characteristics of the electrolyte salt. Preferably it is at least one compound.
As the non-fluorinated cyclic carbonate, one type of the above-described compounds may be used, or two or more types may be used in combination. The content of the non-fluorinated cyclic carbonate is preferably 0 to 50% by mass in the non-aqueous electrolyte, and more preferably 0 to 40% by mass in the non-aqueous electrolyte.

Examples of non-fluorinated chain carbonates include CH ₃ CH ₂ OCOOCH ₂ CH ₃ (diethyl carbonate; DEC), CH ₃ CH ₂ OCOOCH ₃ (methyl ethyl carbonate; MEC), and CH ₃ OCOOCH ₃ (dimethyl carbonate; DMC). , CH ₃ OCOOCH ₂ CH ₂ CH ₃ (methylpropyl carbonate) and other hydrocarbon-based chain carbonates. Of these, DEC, MEC, and DMC are preferred because of their low viscosity and good low-temperature characteristics. The content of the non-fluorinated chain carbonate is preferably 0 to 85% by mass in the non-aqueous electrolyte, and more preferably 0 to 80% by mass in the non-aqueous electrolyte.

When a non-fluorinated cyclic carbonate and a non-fluorinated chain carbonate are used in combination, the content ratio (non-fluorinated cyclic carbonate / non-fluorinated chain carbonate) is 1/15 to 2/1 in volume ratio. Is preferred.
If the proportion of the non-fluorinated cyclic carbonate is too small, the dielectric constant of the entire solvent is lowered, and battery characteristics may be impaired.

The non-aqueous solvent (II) is a combination of a non-fluorinated cyclic carbonate and a non-fluorinated chain carbonate, and a non-fluorinated cyclic carbonate and a non-fluorinated chain carbonate. A combination with a fluorinated ether, a combination of a fluorinated cyclic carbonate, a non-fluorine chain carbonate and a fluorinated ether, or a combination of a fluorinated cyclic carbonate, a fluorinated chain carbonate and a fluorinated ether is preferred.

As the electrolyte salt (III), any salt that can be used for an electrolyte solution for a secondary battery can be used, and among them, a lithium salt is preferable.
Examples of the lithium salt include inorganic lithium salts such as LiClO ₄ , LiPF ₆ and LiBF ₄ ; LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF _{3 SO 2) (C 4 F} 9 SO 2), LiC (CF 3 SO 2) 3, LiPF 4 (CF 3) 2, LiPF 4 (C 2 F 5) 2, LiPF 4 (CF 3 SO 2) 2, LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂ , LiBF ₂ (C ₂ F ₅ SO ₂ ) _2, lithium difluoro (oxalato) borate, lithium bis (oxalato) borate, and the _{formula: LiPF a (C n F 2n} + 1) 6-a ( wherein, a is It is an integer of to 5, n can be mentioned fluorine-containing organic lithium salts such as salts represented by a is) an integer from 1 to 6. These can be used alone or in combination of two or more.

Among these, the lithium salt is capable of suppressing deterioration after the non-aqueous electrolyte is stored at a high temperature, so that LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN ( C ₂ F ₅ SO ₂ ) ₂ , lithium difluoro (oxalate) borate, lithium bis (oxalate) borate, and formula: LiPF _a (C _n F _{2n + 1} ) _{6-a where} a is an integer of 0-5. And n is an integer of 1 to 6, and is preferably at least one selected from the group consisting of salts represented by:

Examples of the salt represented by the formula: LiPF _a (C _n F _{2n + 1} ) _6-a include LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (C ₃ F ₇ ) ₃ LiPF ₃ (C ₄ F ₉ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (C ₃ F ₇ ) ₂ , LiPF ₄ (C ₄ F ₉ ) ₂ And the alkyl group represented by C ₃ F ₇ or C ₄ F ₉ in the formula may be either a straight chain or a branched structure.

The concentration of the electrolyte salt in the nonaqueous electrolytic solution is preferably 0.5 to 3 mol / liter. Outside this range, the electrical conductivity of the electrolytic solution tends to be low, and the battery performance tends to deteriorate.
The concentration of the electrolyte salt is more preferably 0.9 mol / liter or more, and more preferably 1.5 mol / liter or less.

The nonaqueous electrolytic solution of the present invention preferably further contains a 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 can be improved and the battery characteristics 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 terms of better battery characteristics.

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 non-aqueous electrolyte. When there is too much content of the said polyethylene oxide, there exists a possibility that a battery characteristic may be impaired.
The polyethylene oxide content is more preferably 5 × 10 ⁻⁶ mol / kg or more.

The nonaqueous electrolytic solution of the present invention may further contain at least one selected from the group consisting of unsaturated cyclic carbonates, fluorinated cyclic carbonates, and cyclic sulfonic acid compounds. By containing these compounds, deterioration of battery characteristics can be suppressed.

The unsaturated cyclic carbonate is a cyclic carbonate containing an unsaturated bond, and specific examples include vinylene carbonate, 1-methyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, and the like.
The fluorinated cyclic carbonate is a cyclic carbonate to which a fluorine atom is added, and specific examples thereof include fluoroethylene carbonate and difluoroethylene carbonate.
Examples of the cyclic sulfonic acid compound include 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, and the like.
Especially, it is preferable that the non-aqueous electrolyte of this invention contains a 1, 3- propane sultone and a 1, 4- butane sultone from the point which can improve a high temperature characteristic.

The content of these compounds is preferably 0.1 to 10% by mass in the nonaqueous electrolytic solution, more preferably 1% by mass or more, and more preferably 5% by mass or less.

The non-aqueous electrolyte of the present invention is a non-flammable (flame retardant) agent, a surfactant, a highly dielectric additive, a cycle characteristic and a rate characteristic improver, etc., as long as the effects of the present invention are not impaired. May further be contained.

Examples of the incombustible (flame retardant) agent include phosphate esters. 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.

Examples of the flame retardant include (CH ₃ O) ₃ P═O, (CF ₃ CH ₂ O) ₃ P═O, and the like.

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 (3):
Rf ¹ COO ⁻ M ⁺ (3)
(In the formula, Rf ¹ is a fluorine-containing alkyl group which may contain an ether bond having 3 to 10 carbon atoms; M ⁺ is Li ⁺ , Na ⁺ , K ⁺ or NHR ′ ₃ ⁺ (R ′ 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 (4):
Rf ² SO ₃ ⁻ M ⁺ (4)
(In the formula, Rf ² is a fluorine-containing alkyl group which may contain an ether bond having 3 to 10 carbon atoms; M ⁺ is Li ⁺ , Na ⁺ , K ⁺ or NHR ′ ₃ ⁺ (R ′ is the same or different. These are preferably fluorine-containing sulfonates represented by 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 nonaqueous 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.

The nonaqueous electrolytic solution of the present invention preferably contains 0.5 to 70 ppm of hydrofluoric acid. By containing hydrofluoric acid, the film formation of the additive can be promoted.
The content of hydrofluoric acid is more preferably 50 ppm or less, and further preferably 30 ppm or less.
The content of hydrofluoric acid can be measured by a neutralization titration method.

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

Thus, the nonaqueous electrolytic solution of the present invention contains a specific overcharge inhibitor. For this reason, the secondary battery excellent in cycling characteristics and safety | security can be manufactured using the non-aqueous electrolyte of this invention.
Below, a lithium ion secondary battery is demonstrated as an example of the battery using the non-aqueous electrolyte of this invention. Such a lithium ion secondary battery provided with the non-aqueous electrolyte of the present invention is also one aspect of the present invention.

The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, and the non-aqueous electrolyte described above.

A positive electrode is comprised from the positive electrode mixture containing the positive electrode active material which is a material of a positive electrode, and a collector.

The positive electrode active material is particularly preferably a lithium-containing transition metal composite oxide that produces a high voltage.
Examples of the lithium-containing transition metal composite oxide include:
Formula (5): 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 Ge, at least one metal selected from the group consisting of lithium and manganese spinel composite oxides,
Formula (6): 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) , At least one metal selected from the group consisting of Ca, Sr, B, Ga, In, Si and Ge), or
Formula (7): 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, Sr, B, Ga, In, Si, and Ge, at least one metal selected from the group consisting of lithium and cobalt composite oxides.

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 , LiV ₃ Examples include O ₆ , LiNi _0.5 Mn _1.5 O _{4 and the} like.

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 positive electrode active material particles preferably include 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.

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, in view of high battery capacity.

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 Styrene-butadiene rubber, isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, and the like.

Examples of the thickener include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein.

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

Examples of the solvent include N-methyl-2-pyrrolidone, methyl isobutyl ketone, xylene and the like. Of these, N-methyl-2-pyrrolidone is preferable.

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

The 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 negative electrode is composed of a negative electrode mixture containing a negative electrode material and a current collector.

As the negative electrode material, carbonaceous materials capable of occluding and releasing lithium such as organic pyrolysates and artificial graphite and natural graphite under various pyrolysis conditions; lithium such as tin oxide and silicon oxide can be occluded and released Metal oxide materials; lithium metal; various lithium alloys and the like. These negative electrode materials may be used in combination of two or more.

Carbonaceous materials capable of occluding and releasing lithium include artificial graphite or purified natural graphite produced by high-temperature processing of graphitizable pitch obtained from various raw materials, or the surface of these graphite with pitch and other organic substances. Those obtained by carbonizing after the treatment are preferred.

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.
As said thickener, the thing similar to the thickener which can be used for a positive electrode mentioned above is mentioned.

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.

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

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.
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 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.

Thus, the lithium ion secondary battery using the overcharge inhibitor of the present invention can suppress rapid heat generation and ignition during overcharge, and is excellent in safety.
That is, the present invention also provides a step of preparing a non-aqueous electrolyte solution containing a compound represented by the formula (1) and / or a compound represented by the formula (2), and a lithium ion provided with the non-aqueous electrolyte solution. It is also a method for suppressing heat generation during overcharging of a lithium ion secondary battery having a step of manufacturing a secondary battery and a step of charging the lithium ion secondary battery.

The step of preparing the non-aqueous electrolyte containing the compound represented by the formula (1) and / or the compound represented by the formula (2) includes the above-described method for preparing the non-aqueous electrolyte of the present invention. A similar method can be used.
The process of producing a lithium ion secondary battery provided with the said non-aqueous electrolyte can be performed by the method similar to the method of producing the lithium ion secondary battery of this invention mentioned above.
The step of charging the lithium secondary battery is not particularly limited, and can be generally performed by a method similar to a method of charging a known lithium secondary battery.

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

Examples 1-3 and 7, Comparative Examples 1-2
First, a predetermined amount of a cyclic carbonate and a chain carbonate described in Table 1 were mixed in a vertical mixing tank equipped with a stirring blade, and an overcharge inhibitor and a fluoroether described in Table 1 were added thereto. Electrolyte salts and other additives were added to prepare an electrolyte solution having the composition shown in Table 1.
In addition, each component shown in Table 1 is as follows.
(A) Overcharge inhibitor A1:

A2:

A3: cyclohexylbenzene

A4:

A5:

A6:

A7:

(B) Cyclic carbonate B1: Ethylene carbonate (EC)
B2: Vinylene carbonate (VC)
B3: Fluoroethylene carbonate (FEC)

(C) Chain carbonate C1: Methyl ethyl carbonate (MEC)
C2: CF ₃ CH ₂ OCOOCH ₃

(D) Electrolyte salt D1: LiPF ₆

Using the obtained non-aqueous electrolyte, a laminate cell was produced and evaluated for cycle characteristics and safety.

Test 1 (Preparation of laminate cell)
Positive electrode in which LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , carbon black, and polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., trade name: KF-1000) are mixed at 92/3/5 (mass% ratio). The active material was dispersed in N-methyl-2-pyrrolidone to obtain a slurry. This was uniformly coated on a positive electrode current collector (15 μm thick aluminum foil) and dried to form a positive electrode mixture layer. And this was compression-molded with the roller press, it cut | disconnected, the lead body was welded, and the strip | belt-shaped positive electrode was produced.

Separately, styrene-butadiene rubber dispersed in distilled water is added to artificial graphite powder (manufactured by Hitachi Chemical Co., Ltd., trade name MAG-D) so that the solid content becomes 6% by mass, and mixed with a disperser. A slurry was obtained. This was uniformly applied onto a negative electrode current collector (copper foil having a thickness of 10 μm) and dried to form a negative electrode mixture layer. And this was compression-molded with the roller press, cut, and then dried, and the lead body was welded to produce a strip-shaped negative electrode.

As shown in the schematic assembly perspective view of FIG. 1, the belt-like positive electrode 1 is cut into 40 mm × 72 mm (with a 10 mm × 10 mm positive electrode terminal 4), and the belt-like negative electrode 2 is cut into 42 mm × 74 mm (10 mm × 10 mm negative electrode). The lead body was cut to each terminal 5 and a lead body was welded to each terminal. Further, a microporous polyethylene film having a thickness of 20 μm was cut into a size of 78 mm × 46 mm to form a separator 3, and a positive electrode and a negative electrode were set so as to sandwich the separator 3. As shown in FIG. 2, these are placed in an aluminum laminate packaging material 6, and then 2 ml each of the electrolytes prepared in Examples and Comparative Examples are placed in the packaging material 6 and sealed, and a laminate cell having a capacity of about 80 mAh. Was made.

(Cycle characteristics)
In the obtained laminate cell, charging and discharging were performed at 4.35 V at 1.0 C until the charging current became 1/10 C, discharged to 3.0 V at a current equivalent to 0.2 C, and then 1. The cycle was such that charging was performed at 4.35 V at 0 C until the charging current reached 1/10 C. The temperature was 60 ° C.
Charge / discharge is 1 cycle, the discharge capacity after 5 cycles and the discharge capacity after 100 cycles are measured, and the ratio of the discharge capacity after 100 cycles to the discharge capacity after 5 cycles is calculated as the capacity retention rate (%). .

(safety)
The obtained laminated cell was discharged at a current value of 1 CmA at room temperature at a current value of 1 CmA to 3.0 V, wound with glass wool, overcharged at a current value of 1 CmA with 12 V as the upper limit voltage, The presence or absence of ignition / smoke was examined. The case where ignition / smoke has occurred is indicated as x, and the case where it does not occur is indicated as ○.

Examples 4-6, Comparative Example 3
An electrolyte solution was prepared in the same manner as in Example 1 so that the composition described in Table 1 was obtained. Then, a laminate cell was obtained, and cycle characteristics and safety were evaluated.
In the evaluation of cycle characteristics, a positive electrode was prepared using LiNi _0.5 Mn _1.5 O ₄ instead of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , and charge and discharge were performed at 1.0 C. Evaluation was performed in the same manner as in Example 1 except that instead of 4.35 V, the test was performed at 1.0 C and 4.95 V.
Safety was evaluated in the same manner as in Example 1.
The obtained results are shown in Table 1.

From Table 1, it was found that when the electrolytic solution containing the overcharge inhibitor of the present invention was used, the cycle characteristics were excellent and the safety during overcharge was excellent.

The overcharge inhibitor of the present invention can be suitably applied to non-aqueous electrolytes for lithium ion secondary batteries and lithium ion secondary batteries.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode terminal 5 Negative electrode terminal 6 Aluminum laminated packaging material

Claims (5)

Formula (2):

(Wherein R ¹⁴ and R ¹⁵ are the same or different, and both are alkyl groups having 1 to 6 carbon atoms). 2. The overcharge inhibitor according to claim 1, wherein in the compound represented by formula (2), R ¹⁴ and R ¹⁵ are the same or different and both are alkyl groups having 1 to 4 carbon atoms. A nonaqueous electrolytic solution comprising the overcharge inhibitor according to claim 1 or 2, a nonaqueous solvent, and an electrolyte salt. A lithium ion secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte according to claim 3. Formula (2):

(Wherein R ¹⁴ and R ¹⁵ are the same or different and both are alkyl groups having 1 to 6 carbon atoms), and a step of preparing a non-aqueous electrolyte solution containing a compound represented by:
Producing a lithium ion secondary battery comprising the non-aqueous electrolyte, and
And a step of charging the lithium ion secondary battery. A method of suppressing heat generation during overcharging of the lithium ion secondary battery.

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