CN111033862A

CN111033862A - Method for inhibiting decomposition of silyl ester compound

Info

Publication number: CN111033862A
Application number: CN201880051367.2A
Authority: CN
Inventors: 搅上健二; 青山洋平; 野原雄太; 中西真梨惠
Original assignee: Adeka Corp
Current assignee: Adeka Corp
Priority date: 2017-10-11
Filing date: 2018-09-28
Publication date: 2020-04-17
Also published as: JPWO2019073831A1; WO2019073831A1; KR20200067829A

Abstract

The present invention is a method for suppressing decomposition of a silyl ester compound in a nonaqueous electrolytic solution containing a lithium salt containing a fluorine atom, a silyl ester compound selected from the group consisting of a carboxylic acid silyl ester compound, a sulfuric acid silyl ester compound, a sulfonic acid silyl ester compound, a phosphorous acid silyl ester compound, a phosphoric acid silyl ester compound, and a boric acid silyl ester compound, and an organic solvent, wherein a phenylsilane compound represented by the following general formula (1) is incorporated in the nonaqueous electrolytic solution in an amount of 0.1 to 10 mass%, and the moisture content of the nonaqueous electrolytic solution is set to 1000 mass ppm or less. (the definition of each symbol in the formula refers to the description。)

Description

Method for inhibiting decomposition of silyl ester compound

Technical Field

The present invention relates to a method for suppressing decomposition of a silyl ester compound in a nonaqueous electrolytic solution obtained by dissolving a lithium salt containing a fluorine atom and the silyl ester compound in an organic solvent.

Background

With the recent spread of portable personal computers, hand-held video cameras, portable electronic devices for information terminals, and the like, nonaqueous electrolyte secondary batteries having high voltage and high energy density have been widely used as power sources. In view of environmental problems, electric vehicles and hybrid vehicles using electric power as a part of motive power have been put to practical use. Among nonaqueous electrolyte secondary batteries, a secondary battery (so-called lithium ion secondary battery) utilizing insertion and extraction of lithium in charge and discharge reactions is widely used because it can achieve a higher energy density than a lead battery or a nickel-cadmium battery.

In lithium ion secondary batteries, nonaqueous electrolytes obtained by dissolving a lithium salt containing a fluorine atom such as lithium hexafluorophosphate as an electrolyte in a carbonate-based organic solvent such as propylene carbonate or diethyl carbonate have been used, and for the purpose of improving cycle characteristics and the like, nonaqueous electrolytes obtained by further adding a silyl ester compound such as silyl carboxylate (for example, see patent documents 1 to 3), silyl sulfate (for example, see patent documents 4 to 5), silyl sulfonate (for example, see patent documents 4 and 6), silyl phosphate (for example, see

patent documents

5, 7 and 8), or silyl borate (for example, see patent documents 5 and 9) have been studied.

It is known that a lithium salt containing a fluorine atom is slowly hydrolyzed by moisture to generate hydrofluoric acid, and when a silyl ester compound is decomposed by hydrofluoric acid, the cycle characteristics are not improved in some cases. Therefore, as a scavenger of hydrofluoric acid, lactone compounds (for example, see patent document 10), cycloolefin compounds (for example, see patent document 11), silane compounds having SiH groups (for example, see patent document 12), organosilicon compounds having Si — N bonds (for example, see patent document 13), alkoxysilane compounds (for example, see patent document 14), and the like have been studied, but these scavengers have a low rate of trapping hydrofluoric acid and may not effectively inhibit decomposition of silyl ester compounds when the water content in the electrolyte solution is high.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2002-313416

Patent document 2: US2006172200a1

Patent document 3: WO2016/013480 booklet

Patent document 4: US2002197537a1

Patent document 5: japanese patent laid-open publication No. 2006 and 253086

Patent document 6: US2013022861a1

Patent document 7: japanese patent laid-open No. 2001-319685

Patent document 8: japanese patent laid-open publication No. 2004-342607

Patent document 9: japanese patent laid-open No. 2001 and 283908

Patent document 10: japanese patent laid-open No. 2000-182666

Patent document 11: japanese laid-open patent publication No. 2002-

Patent document 12: japanese patent laid-open publication No. 2001-167792

Patent document 13: japanese laid-open patent publication No. 11-016602

Patent document 14: US2016248121a1

Disclosure of Invention

The purpose of the present invention is to suppress the decomposition of a silyl ester compound and improve the storage stability even in the presence of some moisture in a nonaqueous electrolytic solution obtained by dissolving a lithium salt containing a fluorine atom and a silyl ester (silyl ester) compound in an organic solvent.

The present inventors have conducted extensive studies and, as a result, have found that a silane compound having a specific structure has a high effect of suppressing the decomposition of a silyl ester compound, and have completed the present invention.

That is, the present invention is a method for suppressing decomposition of a silyl ester compound in a nonaqueous electrolytic solution containing a lithium salt containing a fluorine atom, a silyl ester compound selected from the group consisting of a carboxylic acid silyl ester compound, a sulfuric acid silyl ester compound, a sulfonic acid silyl ester compound, a phosphorous acid silyl ester compound, a phosphoric acid silyl ester compound and a boric acid silyl ester compound, and an organic solvent, wherein,

a phenylsilane compound represented by the following general formula (1) is mixed in the nonaqueous electrolytic solution in an amount of 0.1-10 mass%, and the water content of the nonaqueous electrolytic solution is set to be less than 1000 mass ppm.

[ chemical formula 1]

(in the formula, R¹、R²、R³、R⁴And R⁵Each independently represents a hydrogen atom, a halogen atom, a nitrile group, a nitro group, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, an oxyalkyl group having 1 to 12 carbon atoms, an acyl group having 1 to 12 carbon atoms or-SiR⁸R⁹R¹⁰A group represented by, R⁶、R⁷、R⁸、R⁹And R¹⁰Independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, and X¹Represents a hydrocarbon group having a valence of m, and m represents a number of 1 to 3. )

Drawings

Fig. 1 is a longitudinal sectional view schematically showing an example of the structure of a coin-type battery as a secondary battery as an example of the use of a nonaqueous electrolytic solution in the method of the present invention.

Fig. 2 is a schematic diagram showing a basic configuration of a cylindrical battery as a secondary battery as an example of the use of the nonaqueous electrolytic solution in the method of the present invention.

Fig. 3 is a perspective view showing an internal structure of a cylindrical battery of a secondary battery in a cross section as an example of the use of the nonaqueous electrolytic solution in the method of the present invention.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described.

In the general formula (1), R¹、R²、R³、R⁴And R⁵(hereinafter also referred to as "R")¹～R⁵". ) Each independently represents a hydrogen atom, a halogen atom, a nitrile group, a nitro group, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, an oxyalkyl group having 1 to 12 carbon atoms, an acyl group having 1 to 12 carbon atoms or-SiR⁸R⁹R¹⁰The group shown. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom and the like.

Examples of the alkyl group having 1 to 12 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, a 1-methylbutyl group, an isohexyl group, a 2-ethylhexyl group, and a 2-methylhexyl group.

Examples of the alkenyl group having 2 to 12 carbon atoms include a vinyl group, an allyl group, a 1-butenyl group, a 2-butenyl group, a 3-butenyl group, a1, 3-butadienyl group, a 1-methylvinyl group, a 2-methylvinyl group, a 1-methylallyl group, a1, 1-dimethylallyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, and a dodecenyl group.

Examples of the cycloalkyl group having 5 to 12 carbon atoms include cyclopentyl, cyclohexyl, and 2-norbornenyl.

Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a biphenyl group, a naphthyl group, a tolyl group, a xylyl group, a trimethylphenyl group, an ethylphenyl group and the like.

Examples of the aralkyl group having 7 to 12 carbon atoms include a benzyl group, a phenylethyl group, a phenylpropyl group, a tolylmethyl group, a tolylethyl group, a tolylpropyl group, a ditolylmethyl group, and a ditolylpropyl group.

Examples of the oxyalkyl group having 1 to 12 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, an octyloxy group, a decyloxy group and the like.

Examples of the acyl group having 1 to 12 carbon atoms include formyl group, acetyl group, propionyl group, butyryl group, pentanoyl group, hexanoyl group, heptanoyl group, octanoyl group, nonanoyl group, decanoyl group, undecanoyl group, and dodecanoyl group.

R⁶、R⁷、R⁸、R⁹And R¹⁰(hereinafter also referred to as "R")⁶～R¹⁰". ) Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms. Examples of the alkyl group having 1 to 12 carbon atoms, the alkenyl group having 2 to 12 carbon atoms, the cycloalkyl group having 5 to 12 carbon atoms, the aryl group having 6 to 12 carbon atoms and the aralkyl group having 7 to 12 carbon atoms include R¹～R⁵The alkyl group having 1 to 12 carbon atoms, the alkenyl group having 2 to 12 carbon atoms, the cycloalkyl group having 5 to 12 carbon atoms, the aryl group having 6 to 12 carbon atoms and the aralkyl group having 7 to 12 carbon atoms are exemplified in (A) and (B).

As R¹～R⁵From the viewpoint of easy availability of industrial raw materials, preferred is a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms or-SiR⁸R⁹R¹⁰Further, a hydrogen atom or a fluorine atom is preferable. In addition, R is also preferable¹～R ⁵1 to 2 of them are-SiR⁸R⁹R¹⁰. In this case, the remaining R is preferred¹～R⁵Is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and the remaining R is particularly preferred¹～R⁵Is a hydrogen atom.

As R⁶And R⁷In view of easy availability of industrial raw materials, an alkyl group having 1 to 4 carbon atoms or a phenyl group is preferable, and a methyl group is more preferable.

As R⁸、R⁹And R¹⁰In view of easy availability of industrial raw materials, an alkyl group having 1 to 4 carbon atoms or a phenyl group is preferable, and a methyl group is more preferable.

X¹Represents a hydrocarbon group having a valence of m, and m represents a number of 1 to 3. Examples of the 1-valent hydrocarbon group in which m is a number of 1 include R¹～R⁵The alkyl group having 1 to 12 carbon atoms, the alkenyl group having 2 to 12 carbon atoms, the cycloalkyl group having 5 to 12 carbon atoms, the aryl group having 6 to 12 carbon atoms and the aralkyl group having 7 to 12 carbon atoms are exemplified in (A) and (B).

Examples of the 2-valent hydrocarbon group in which m is a number of 2 include alkane diyl groups having 1 to 10 carbon atoms such as methane-1, 1-diyl group, ethane-1, 2-diyl group, ethane-1, 1-diyl group, propane-1, 3-diyl group, propane-1, 2-diyl group, butane-1, 4-diyl group, 2-methylpropane-1, 3-diyl group, 2-dimethylpropane-1, 3-diyl group, pentane-1, 5-diyl group, hexane-1, 6-diyl group, heptane-1, 7-diyl group, octane-1, 8-diyl group, nonane-1, 9-diyl group, decane-1, 10-diyl group, and the like; a group represented by the following general formula (6), a group represented by the following general formula (7), and the like. One or more methylene groups other than both ends of the alkanediyl group having 3 or more carbon atoms may be substituted with-S-or-O-.

[ chemical formula 2]

(in the formula, R⁴⁵And R⁴⁶Each independently represents a carbon atom number of1 to 10 alkanediyl groups or a direct bond. )

[ chemical formula 3]

(in the formula, R⁴⁷And R⁴⁸Each independently represents an alkanediyl group having 1 to 10 carbon atoms or a direct bond. )

Examples of the 3-valent hydrocarbon group in which m is a number of 3 include alkanetriyl groups having 1 to 10 carbon atoms such as methane-1, 1, 1-triyl, ethane-1, 1, 1-triyl, propane-1, 2, 3-triyl, pentane-1, 3, 5-triyl, hexane-1, 1-triyl, octane-1, 1, 1-triyl, decane-1, 1, 1-triyl, and the like; a group represented by the following general formula (8), a group represented by the following general formula (9), and the like.

[ chemical formula 4]

(in the formula, R⁴⁹、R⁵⁰And R⁵¹Each independently represents an alkanediyl group having 1 to 10 carbon atoms or a direct bond. )

[ chemical formula 5]

(in the formula, R⁵²、R⁵³And R⁵⁴Each independently represents an alkanediyl group having 1 to 10 carbon atoms or a direct bond. )

As R⁴⁵、R⁴⁶、R⁴⁷、R⁴⁸、R⁴⁹、R⁵⁰、R⁵¹、R⁵²、R⁵³And R⁵⁴The alkanediyl group having 1 to 10 carbon atoms is exemplified by X¹Examples of the group include alkanediyl groups having 1 to 10 carbon atoms, and the groups exemplified above.

Among the phenylsilane compounds represented by the general formula (1), particularly preferred compounds include trimethylphenylsilane, triethylphenylsilane, dimethyldiphenylsilane, methyltriphenylsilane, trimethyl-4-fluorophenylsilane, trimethyl-2, 4, 6-trifluorophenylsilane, butyldimethylphenylsilane, dimethyloctylphenylsilane, 1, 4-bis (trimethylsilyl) benzene, 1, 2-bis (trimethylsilyl) benzene, 1, 4-bis (dimethylphenylsilyl) benzene, 1,1, 1-tris (dimethylphenylsilyl) ethane and the like.

The addition amount of the phenylsilane compound represented by the general formula (1) in the nonaqueous electrolytic solution is preferably 0.1 to 10% by mass. By setting the amount of addition to 0.1 mass% or more, sufficient effects are easily exhibited, and by setting the amount to 10 mass% or less, an incremental effect commensurate with the amount of addition is easily obtained, and the possibility of degradation of battery performance due to an increase can be prevented. The addition amount of the phenylsilane compound represented by the general formula (1) in the nonaqueous electrolytic solution is more preferably 0.1 to 7% by mass, still more preferably 0.5 to 7% by mass, and most preferably 1 to 5% by mass.

The timing of mixing the phenylsilane compound represented by the general formula (1) in the nonaqueous electrolytic solution is not limited, and the phenylsilane compound may be mixed in the nonaqueous electrolytic solution together with the lithium salt, the silyl ester compound, and the organic solvent. For example, the nonaqueous electrolytic solution may be prepared by mixing any one of the lithium salt, the silyl ester compound, and the organic solvent with the phenylsilane compound and then mixing the other materials, or may be prepared by mixing a material other than the lithium salt, the silyl ester compound, and the organic solvent with the phenylsilane compound and then mixing the lithium salt, the silyl ester compound, and the organic solvent.

[ lithium salt containing fluorine atom ]

The method for suppressing the decomposition of a silyl ester compound of the present invention is a method for suppressing the decomposition of a silyl ester compound in a nonaqueous electrolytic solution in which a lithium salt containing a fluorine atom and the silyl ester compound are dissolved in an organic solvent. The lithium salt containing a fluorine atom is a component to be mixed as an electrolyte of the nonaqueous electrolytic solution. The lithium salt containing a fluorine atom includes LiPF₆、LiBF₄、LiPO₂F₂、LiAsF₆、Li₂SiF₆、LiSbF₆、LiN(SO₂F)₂、LiOSO₂Rf { wherein Rf represents a fluorocarbon group }, and LiN (SO)₂Rf)₂{ wherein Rf represents a fluorocarbon group }, and LiPF_a(Rf)_6-a{ wherein Rf represents a fluorocarbon group, and a represents a number of 0 to 5 }, and the like. The lithium salt containing a fluorine atom to be used as the nonaqueous electrolytic solution to which the phenylsilane compound of the present invention is applied is preferably LiPF because excellent battery performance can be obtained, while decomposition of the silyl ester compound is likely to occur, and the decomposition-inhibiting effect by the phenylsilane compound of the present invention is large₆、LiBF₄、Li₂SiF₆、LiSbF₆、LiN(SO₂F)₂、LiOSO₂CF₃、LiN(SO₂CF₃)₂、LiN(SO₂CF₂CF₃)₂Further preferably LiPF₆、LiBF₄、LiN(SO₂F)₂、LiOSO₂CF₃、LiN(SO₂CF₃)₂、LiN(SO₂CF₂CF₃)₂Most preferably LiPF₆、LiBF₄、LiN(SO₂CF₃)₂。

The electrolyte in the nonaqueous electrolytic solution may contain an electrolyte other than the lithium salt containing a fluorine atom, but since the decomposition of the silyl ester compound becomes difficult to occur and the decomposition-suppressing effect by the phenylsilane compound of the present invention becomes difficult to obtain when the proportion of the lithium salt containing a fluorine atom in the electrolyte is low, the proportion of the lithium salt containing a fluorine atom is preferably at least 20 mol% with respect to the entire electrolyte. Examples of the electrolyte other than the lithium salt containing a fluorine atom include LiClO₄LiCl, LiBr, etc. The concentration of the electrolyte in the nonaqueous electrolytic solution is preferably 0.1 to 7mol/L, and more preferably 0.5 to 1.8 mol/L. When the electrolyte concentration is in this range, the safety can be improved, and a battery having high reliability and contributing to reduction of environmental load can be obtained.

[ silyl ester Compound ]

Examples of the silyl ester compound include a carboxylic acid silyl ester compound, a sulfuric acid silyl ester compound, a sulfonic acid silyl ester compound, a phosphorous acid silyl ester compound, a phosphoric acid silyl ester compound, and a boric acid silyl ester compound. The content of the silyl ester compound in the nonaqueous electrolytic solution is preferably 0.01 to 7% by mass, more preferably 0.1 to 5% by mass, and most preferably 0.3 to 3% by mass.

Examples of the carboxylic acid silyl ester compound include compounds represented by the following general formula (2).

[ chemical formula 6]

(in the formula, R¹¹、R¹²And R¹³Independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, and X²Represents a direct bond or a group having a valence of n, and n represents a number of 1 to 4. )

In the general formula (2), R¹¹、R¹²And R¹³(hereinafter also referred to as "R")¹¹～R¹³". ) Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms. Examples of such a group include R of the general formula (1)⁶～R¹⁰The groups exemplified in (1). As R¹¹～R¹³From the viewpoint of easy availability of industrial raw materials, methyl or phenyl is preferred, and methyl is more preferred.

X²Represents a group having a valence of n, and n represents a number of 1 to 4.

As X when n is 1²In addition to X when m is 1 in the general formula (1)¹Examples of the groups listed in the aboveIn addition to the same groups, a heterocyclic group having 2 to 12 carbon atoms and having a valence of 1 may be mentioned. The heterocyclic group having 2 to 12 carbon atoms and having a valence of 1 is preferably a group having 3 to 9 carbon atoms, and examples thereof include a group having a valence of 1 derived from a heterocyclic ring such as a pyrrole ring, furan ring, thiophene ring, pyrrolidine ring, tetrahydrofuran ring, tetrahydrothiophene ring, piperidine ring, tetrahydropyran ring, tetrahydrothiopyran ring, imidazole ring, pyrazole ring, oxazole ring, thiazole ring, imidazoline ring, pyrazine ring, morpholine ring, or thiazine ring, or a polynuclear heterocyclic ring of these heterocyclic rings and benzene rings.

In the case where n is 1, X²Preferably an alkyl group having 2 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, a cycloalkyl group having 6 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 9 carbon atoms or a heterocyclic group having 2 to 5 carbon atoms, and particularly preferably an alkenyl group having 2 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms or an aralkyl group having 7 to 9 carbon atoms.

As X when n is 2²In addition to X when m is 2 in the general formula (1)¹Examples of the (C) group include, in addition to the same groups as those listed above, a direct bond, an alkylenediyl group having 2 to 10 carbon atoms, and a heterocyclic group having 2 to 12 carbon atoms and having a valence of 2. Examples of the alkenediyl group having 2 to 10 carbon atoms include ethylene-1, 1-diyl, ethylene-1, 2-diyl, propylene-1, 3-diyl, propylene-2, 3-diyl, 1-butene-1, 2-diyl, 1-butene-1, 3-diyl, 1-butene-1, 4-diyl, 2-pentene-1, 5-diyl, and 3-hexene-1, 6-diyl. Examples of the heterocyclic group having 2-12 carbon atoms and having a valence of 2 include X when n is 1²The 2-valent group derived from the heterocyclic ring or polynuclear heterocyclic ring mentioned in (1) is preferably a group having 3 to 9 carbon atoms.

In the case where n is 2, X²Preferably a C2-6 alkanediyl group, a C2-6 alkenediyl group, a group represented by the general formula (6) or (7), a 2-valent C2-5 heterocyclic group, particularly preferably a C2-6 alkanediyl group, a C2-6 alkenediyl group, a C2-valent C2-5 heterocyclic group2 to 5 heterocyclic groups. As mentioned above, the methylene group in the alkanediyl group may be substituted by-S-or-O-.

As X when n is 3²In addition to X when m is 3 in the general formula (1)¹Examples of the (C) group include heterocyclic groups having 2 to 12 carbon atoms and having a valence of 3 in addition to the same groups as those listed above. Examples of the heterocyclic group having 2 to 12 carbon atoms and having a valence of 3 include X when n is 1²The heterocyclic or polynuclear heterocyclic group having a valence of 3 in the above-mentioned groups preferably has 3 to 9 carbon atoms.

As X when n is 4²X is 1 to 3 inclusive of n²The corresponding group having a valence of 4.

In the case where n is 3, X²Preferably an alkanetriyl group having 3 to 6 carbon atoms, a group represented by general formula (8) or (9), or a heterocyclic group having 2 to 5 carbon atoms and having 3 valence, and particularly preferably a group represented by general formula (9) or a heterocyclic group having 2 to 5 carbon atoms and having 3 valence.

In the case where n is 4, X²Preferably an alkanetetrayl group having 4 to 6 carbon atoms, an aromatic ring-containing group having 6 to 10 carbon atoms and having 4 valence, or a heterocyclic group having 2 to 5 carbon atoms and having 4 valence.

In the present specification, when a "heterocyclic group-containing group having 2 to 12 carbon atoms" is referred to, the "carbon number is 2 to 12" herein does not specify the carbon number of only one of the heterocyclic groups but specifies the carbon number of the entire heterocyclic group-containing group.

The compound represented by the general formula (2) may be a silyl ester of a carboxylic acid compound represented by the following general formula (2a), and the compound represented by the general formula (2) can be obtained by silyl esterification of the carboxyl group of the carboxylic acid compound represented by the general formula (2a) by a known method.

[ chemical formula 7]

(in the formula, X²And n is as defined for formula (1). )

In the carboxylic acid compound represented by the general formula (2a), examples of monocarboxylic acids in which n is 1 include acetic acid, propionic acid, butyric acid, valeric acid, isovaleric acid, caproic acid, enanthic acid, caprylic acid, acrylic acid, methacrylic acid, crotonic acid, benzoic acid, methylbenzoic acid, 4-tert-butylbenzoic acid, naphthalenecarboxylic acid, phenylacetic acid, naphthylacetic acid, 4-methoxybenzoic acid, 2-thiophenecarboxylic acid, picolinic acid, and nicotinic acid.

Examples of the dicarboxylic acid in which n is 2 include dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, muconic acid, dihydromuconic acid, acetylene dicarboxylic acid, 4-cyclohexene-1, 2-dicarboxylic acid, 1, 2-cyclohexanedicarboxylic acid, 1, 4-cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid, terephthalic acid, 2 ' -thiodiacetic acid, ethylenedithiodiacetic acid, 3 ' -thiodipropionic acid, 3 ' -dithiodipropionic acid, 2, 5-thiophenedicarboxylic acid, 3, 4-thiophenedicarboxylic acid, adamantanedicarboxylic acid, 2, 5-furandicarboxylic acid, and dipicolinic acid.

Examples of the tricarboxylic acid in which n is 3 include propane-1, 2, 3-tricarboxylic acid, pentane-1, 3, 5-tricarboxylic acid, benzene-1, 2, 3-tricarboxylic acid, benzene-1, 2, 4-tricarboxylic acid, benzene-1, 3, 5-tricarboxylic acid, thiophene-2, 3, 5-tricarboxylic acid, 1,3, 5-trithiane-2, 4, 6-tricarboxylic acid, and the like.

Examples of the tetracarboxylic acid in which n is a number of 4 include dodecane-1, 1,12, 12-tetracarboxylic acid, cyclopentane-1, 2,3, 4-tetracarboxylic acid, benzene-1, 2,4, 5-tetracarboxylic acid, tetrahydrofuran-2, 3,4, 5-tetracarboxylic acid, and thiophene-2, 3,4, 5-tetracarboxylic acid.

Examples of the silyl sulfate compound and the silyl sulfonate compound include compounds represented by the following general formula (3).

[ chemical formula 8]

(in the formula, R¹⁴、R¹⁵、R¹⁶And R¹⁷Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, and p represents a number of 0 or 1. )

In the general formula (3), R¹⁴、R¹⁵、R¹⁶And R¹⁷(hereinafter also referred to as "R")¹⁴～R¹⁷". ) Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms. Examples of such a group include R of the general formula (1)⁶～R¹⁰The groups exemplified in (1). p represents a number of 0 or 1, and when p is a number of 0, the compound represented by the general formula (3) is a silyl sulfate compound, and when p is a number of 1, it is a silyl sulfonate compound.

As R¹⁴In view of easy availability of industrial raw materials, an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 10 carbon atoms is preferable. As R¹⁵、R¹⁶And R¹⁷From the viewpoint of easy availability of industrial raw materials, an alkyl group having 1 to 4 carbon atoms or a phenyl group is preferable, a methyl group or a phenyl group is more preferable, and a methyl group is particularly preferable.

When p in the general formula (3) is a number of 0, that is, when the compound represented by the general formula (3) is a silyl sulfate compound, preferable examples of the compound include bis (trimethylsilyl) sulfate, bis (dimethylphenylsilyl) sulfate, bis (methyldiphenylsilyl) sulfate, bis (triphenylsilyl) sulfate, and the like.

When p in the general formula (3) is a number of 1, that is, when the compound represented by the general formula (3) is a silyl sulfonate compound, preferable compounds include trimethylsilyl methanesulfonate, dimethylphenylsilyl methanesulfonate, trimethylsilyl benzenesulfonate, trimethylsilyl toluenesulfonate, and the like.

Examples of the silyl phosphite compound and the silyl phosphate compound include compounds represented by the following general formula (4).

[ chemical formula 9]

(in the formula, R¹⁸、R¹⁹、R²⁰、R²¹、R²²、R²³、R²⁴、R²⁵And R²⁶Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, and q represents a number of 0 or 1. )

In the general formula (4), R¹⁸、R¹⁹、R²⁰、R²¹、R²²、R²³、R²⁴、R²⁵And R²⁶(hereinafter also referred to as "R")¹⁸～R²⁶") independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms. Examples of such a group include R of the general formula (1)⁶～R¹⁰The groups exemplified in (1). As R¹⁸～R²⁶From the viewpoint of easy availability of industrial raw materials, an alkyl group having 1 to 4 carbon atoms or a phenyl group is preferable, a methyl group or a phenyl group is more preferable, and a methyl group is particularly preferable. q represents a number of 0 or 1, and when q is a number of 0, the compound represented by the general formula (4) is a silyl phosphite compound, and when q is a number of 1, it is a silyl phosphate compound.

When q in the general formula (4) is a number of 0, that is, when the compound represented by the general formula (4) is a silyl phosphite compound, preferable compounds include tris (trimethylsilyl) phosphite, tris (dimethylphenylsilyl) phosphite, tris (methyldiphenylsilyl) phosphite, tris (triphenylsilyl) phosphite, and the like.

When q in the general formula (4) is a number of 1, that is, when the compound represented by the general formula (4) is a silyl phosphate compound, preferable examples of the compound include tris (trimethylsilyl) phosphate, tris (dimethylphenylsilyl) phosphate, tris (methyldiphenylsilyl) phosphate, and tris (triphenylsilyl) phosphate.

Examples of the silyl borate compound include compounds represented by the following general formula (5).

[ chemical formula 10]

(in the formula, R²⁷、R²⁸、R²⁹、R³⁰、R³¹、R³²、R³³、R³⁴And R³⁵Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms. )

In the general formula (5), R²⁷、R²⁸、R²⁹、R³⁰、R³¹、R³²、R³³、R³⁴And R³⁵(hereinafter also referred to as "R")²⁷～R³⁵") independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms. Examples of such a group include R of the general formula (1)⁶～R¹⁰The groups exemplified in (1). As R²⁷～R³⁵From the viewpoint of easy availability of industrial raw materials, an alkyl group having 1 to 4 carbon atoms or a phenyl group is preferable, a methyl group or a phenyl group is more preferable, and a methyl group is particularly preferable.

Preferable examples of the compound represented by the general formula (5) include tris (trimethylsilyl) borate, tris (dimethylphenylsilyl) borate, tris (methyldiphenylsilyl) borate, and tris (triphenylsilyl) borate.

[ organic solvent ]

As the organic solvent used in the nonaqueous electrolytic solution in the method for suppressing decomposition of a silyl ester compound of the present invention, 1 kind of organic solvent generally used in nonaqueous electrolytic solutions may be used or 2 or more kinds may be used in combination. Specific examples thereof include carbonate solvents, ester solvents, ether solvents, sulfoxide solvents, and the like.

Examples of the carbonate-based solvent include saturated chain carbonate compounds such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl butyl carbonate, methyl t-butyl carbonate, diisopropyl carbonate, and t-butyl propyl carbonate; saturated cyclic carbonate compounds such as ethylene carbonate, 1-fluoroethylene carbonate, 1, 2-propylene carbonate, 1, 3-propylene carbonate, 1, 2-butylene carbonate, 1, 3-butylene carbonate, 1-dimethylethylene carbonate, 1, 2-bis (methoxycarbonyloxy) ethane, 1, 2-bis (ethoxycarbonyloxy) ethane and 1, 2-bis (ethoxycarbonyloxy) propane, and the like.

Examples of the ester solvent include saturated cyclic ester compounds such as γ -butyrolactone, γ -valerolactone, γ -caprolactone, δ -caprolactone and δ -octalactone; and saturated chain ester compounds such as methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl pivalate, ethyl pivalate, methyl malonate, ethyl malonate, methyl succinate, ethyl succinate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethylene glycol diacetyl, and propylene glycol diacetyl.

Examples of the ether solvent include chain ether compounds such as dimethoxyethane, ethoxymethoxyethane, diethoxyethane, ethylene glycol bis (trifluoroethyl) ether, propylene glycol bis (trifluoroethyl) ether, ethylene glycol bis (trifluoromethyl) ether, and diethylene glycol bis (trifluoroethyl) ether; cyclic ether compounds such as tetrahydrofuran, dioxolane and dioxane.

Examples of the sulfoxide-based solvent include dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, diphenyl sulfoxide, and thiophene. Examples of the sulfone-based solvent include dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone, sulfolane (also referred to as tetramethylene sulfone), 3-methylsulfolane, 3, 4-dimethylsulfolane, 3, 4-diphenylmethylsulfolane, sulfolene, 3-methylsulfolane, 3-ethylsulfolene and 3-bromomethylsulfolane. Examples of the amide solvent include N-methylpyrrolidone, dimethylformamide, and dimethylacetamide. In addition, acetonitrile, propionitrile, nitromethane, or a derivative thereof may be used as the organic solvent.

In the method for suppressing decomposition of a silyl ester compound of the present invention, decomposition of the silyl ester compound can be suppressed efficiently when the moisture content in the nonaqueous electrolytic solution is 1000ppm by mass or less. When the moisture content is more than 1000 mass ppm, it becomes difficult to suppress the decomposition of the silyl ester compound. The water content in the nonaqueous electrolytic solution is preferably 500 mass ppm or less, and more preferably 300 mass ppm or less. The moisture content of the nonaqueous electrolytic solution can be measured by karl fischer titration or the like. The moisture content of the nonaqueous electrolytic solution may be measured at any time as long as the nonaqueous electrolytic solution contains a lithium salt containing a fluorine atom, a silyl ester compound, an organic solvent, and a phenylsilane compound represented by the general formula (1).

The moisture in the nonaqueous electrolytic solution causes decomposition of the silyl ester compound, but the moisture is not only mixed in from the raw material of the nonaqueous electrolytic solution, but also mixed in at the time of production of the nonaqueous electrolytic solution or at the time of assembly of the battery. Therefore, in the case of producing a nonaqueous electrolytic solution, it is not sufficient to use only a raw material having a small water content, and it is necessary to produce the nonaqueous electrolytic solution in an inert gas atmosphere, a low-humidity atmosphere, or the like, and to perform a sufficient dehydration treatment after the production. In addition, the battery needs to be mounted in a low-humidity atmosphere (for example, in a dry room) during the mounting of the battery, and a large cost is required for setting the low-humidity atmosphere. According to the method for suppressing decomposition of a silyl ester compound of the present invention, the cost required for dehydration treatment of a nonaqueous electrolytic solution or the cost required for a low humidity atmosphere can be reduced.

In order to set the water content in the nonaqueous electrolytic solution to 1000ppm or less, it is sufficient to blow an inert gas after drying into the nonaqueous electrolytic solution, as described in examples described later, or the like. As the inert gas, nitrogen gas can be cited.

In the method for suppressing decomposition of a silyl ester compound of the present invention, when the moisture content in the nonaqueous electrolytic solution is higher than a certain value, the silyl ester compound is likely to be decomposed, and therefore the phenylsilane compound of the present invention is likely to further exhibit the effect of suppressing decomposition. Therefore, in the method for suppressing decomposition of the silyl ester compound of the present invention, the moisture content of the nonaqueous electrolytic solution is preferably 5 ppm by mass or more, more preferably 10 ppm by mass or more, and still more preferably 20 ppm by mass or more. In a secondary battery such as a lithium ion secondary battery, a laminate of a heat-fusible film and an aluminum foil is used as an outer covering member in order to prevent moisture from penetrating into the nonaqueous electrolytic solution from the outer covering portion, but the moisture may not be completely blocked and may slowly penetrate into the nonaqueous electrolytic solution from the outer covering portion. Therefore, even when the moisture in the nonaqueous electrolytic solution of the assembled secondary battery is not contained so as to immediately cause the decomposition of the silyl ester compound, it is preferable to add 0.1 to 10 mass% of the phenylsilane compound represented by the general formula (1) to the nonaqueous electrolytic solution in order to prevent the moisture from entering the exterior package.

The nonaqueous electrolytic solution obtained by the method for suppressing decomposition of a silyl ester compound of the present invention can be suitably used for conventionally known nonaqueous electrolytic solution secondary batteries, particularly lithium ion secondary batteries.

As the positive electrode, a sheet-like positive electrode is used which is obtained by coating a current collector with a slurry of a positive electrode active material, a binder and a conductive material in an organic solvent or water and drying the coating.

As the positive electrode active material, the followingFor example, a known positive electrode active material capable of inserting and extracting lithium as an electrode reactant can be used for a lithium ion secondary battery. Examples of the known positive electrode active material include a lithium transition metal complex oxide, a lithium-containing transition metal phosphate compound, a metal oxide, a metal sulfide, a metal halide, a metal interlayer compound, and sulfur, and they may be used in combination. As the transition metal of the lithium transition metal composite oxide, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, and the like are preferable. Specific examples of the lithium transition metal composite oxide include LiCoO₂Lithium cobalt composite oxide, LiNiO, etc₂Lithium nickel composite oxide and LiMnO₂、LiMn₂O₄、Li₂MnO₃And lithium manganese complex oxides, and those obtained by substituting a part of transition metal atoms that are the main components of these lithium transition metal complex oxides with another metal such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, and zirconium. Specific examples of the substance obtained by substitution include, for example, Li_1.1Mn_1.8Mg_0.1O₄、Li_1.1Mn_1.85Al_0.05O₄、LiNi_0.5Co_0.2Mn_0.3O₂、LiNi_0.8Co_0.1Mn_0.1O₂、LiNi_0.5Mn_0.5O₂、LiNi_0.80Co_0.17Al_0.03O₂、LiNi_0.80Co_0.15Al_0.05O₂、LiNi_1/3Co_1/ ₃Mn_1/3O₂、LiNi_0.6Co_0.2Mn_0.2O₂、LiMn_1.8Al_0.2O₄、LiMn_1.5Ni_0.5O₄、Li₂MnO₃-LiMO₂And (M ═ Co, Ni, Mn) and the like. The transition metal of the lithium-containing transition metal phosphate compound is preferably vanadium, titanium, manganese, iron, cobalt, nickel, or the like, and specific examples thereof include LiFePO₄Iso-phosphates, LiCoPO₄Cobalt phosphates, phosphorus to be the lithium transition metalAnd those obtained by substituting a part of transition metal atoms in the main body of the acid compound with another metal such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, zirconium, niobium, and the like. The surface of the positive electrode active material may be covered with a conductive material described later as necessary.

Examples of the binder include Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), styrene-isoprene copolymer, polymethyl methacrylate, polyacrylate, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), Methyl Cellulose (MC), starch, polyvinyl pyrrolidone, Polyethylene (PE), polypropylene (PP), polyethylene oxide (PEO), Polyimide (PI), polyamide imide (PAI), Polyacrylonitrile (PAN), polyvinyl chloride (PVC), polyacrylic acid, and polyurethane. The amount of the binder used is usually about 1 to 50% by mass, preferably 2 to 20% by mass, based on the positive electrode active material.

Examples of the conductive material include carbon materials such as fine particles of graphite, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon nanotubes, vapor-phase carbon fibers, graphene, and needle coke; metal powders such as aluminum powder, nickel powder, titanium powder, and the like; conductive metal oxides such as zinc oxide and titanium oxide; la₂S₃、Sm₂S₃、Ce₂S₃、TiS₂Etc. sulfur-containing conductive materials, etc. The amount of the conductive material used is usually about 0.5 to 30% by mass, preferably 1 to 15% by mass, based on the positive electrode active material.

As the solvent for slurrying, an organic solvent or water in which the binder is dissolved is used. Examples of the organic solvent include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. The amount of the solvent used is usually about 20 to 400 mass%, preferably 30 to 200 mass%, based on the positive electrode active material.

As the current collector of the positive electrode, aluminum, stainless steel, nickel-plated steel, or the like is generally used.

As the negative electrode, a sheet-like negative electrode obtained by applying a current collector with a substance obtained by slurrying a negative electrode active material, a binder, and a conductive material with an organic solvent or water and drying the resultant is generally used.

Examples of the negative electrode active material include carbonaceous materials, lithium alloys, silicon alloys, silicon oxide, tin alloys, tin oxide, phosphorus, germanium, indium, copper oxide, antimony sulfide, titanium oxide, iron oxide, manganese oxide, cobalt oxide, nickel oxide, lead oxide, ruthenium oxide, tungsten oxide, and zinc oxide, and further include LiVO₂、Li₂VO₄、Li₄Ti₅O₁₂And composite oxides, conductive polymers, and the like. The carbonaceous material is not particularly limited, and examples thereof include crystalline carbon such as natural graphite, artificial graphite, fullerene, graphene, broken graphite fibers, carbon nanotubes, graphite whiskers, highly oriented pyrolytic graphite, kish graphite, hard graphitizable carbon, easy graphitizable carbon, petroleum coke, coal coke, petroleum pitch carbide, coal pitch carbide, phenol resin, crystalline cellulose resin carbide, and the like, and carbon materials obtained by partially carbonizing these, furnace black, acetylene black, pitch carbon fibers, PAN carbon fibers, and the like.

Examples of the binder, the conductive material, and the solvent to be slurried include the same ones as those of the positive electrode. The amount of the binder used is usually about 0.1 to 30% by mass, preferably about 0.5 to 15% by mass, based on the negative electrode active material. The amount of the solvent used is usually about 25 to 400 mass%, preferably 30 to 200 mass%, based on the negative electrode active material.

As the current collector of the negative electrode, copper, nickel, stainless steel, nickel-plated steel, or the like is generally used.

In the nonaqueous electrolyte secondary battery of the present invention, a separator is used between the positive electrode and the negative electrode, and a generally used polymer microporous membrane can be used as the separator without particular limitation. Examples of the membrane include membranes formed of a polymer compound or a derivative thereof, a copolymer or a mixture thereof mainly composed of polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyethers such as polyethylene oxide and polypropylene oxide, various celluloses such as carboxymethyl cellulose and hydroxypropyl cellulose, poly (meth) acrylic acid and various esters thereof, and the like. These films may be used alone, or these films may be stacked to form a multilayer film. Further, in these films, various additives may be used, and the kind or content thereof is not particularly limited. Among these films, a film made of polyethylene, polypropylene, polyvinylidene fluoride, or polysulfone is preferably used for the nonaqueous electrolyte secondary battery of the present invention. These membranes are made microporous so that ions can easily permeate through the membranes by permeation of the electrolyte. In addition, for the purpose of improving safety, it may be coated with ceramics such as alumina or silica.

In the nonaqueous electrolyte secondary battery of the present invention, a phenolic antioxidant, a phosphorus antioxidant, a thioether antioxidant, a hindered amine compound, or the like may be added to the electrode material, the nonaqueous electrolyte, and the separator for the purpose of further improving safety.

The shape of the nonaqueous electrolyte secondary battery of the present invention including the above-described configuration is not particularly limited, and the nonaqueous electrolyte secondary battery may be formed into various shapes such as a coin shape, a cylinder shape, a square shape, a laminate shape, and the like. Fig. 1 is a view showing an example of a coin-type battery of a nonaqueous electrolyte secondary battery of the present invention, and fig. 2 and 3 are views showing an example of a cylinder-type battery.

In a coin-type nonaqueous electrolyte secondary battery 10 shown in fig. 1,1 is a positive electrode capable of releasing lithium ions, 1a is a positive electrode current collector, 2 is a negative electrode made of a carbonaceous material capable of inserting and releasing lithium ions released from the positive electrode, 2a is a negative electrode current collector, 3 is the nonaqueous electrolyte of the present invention, 4 is a positive electrode case made of stainless steel, 5 is a negative electrode case made of stainless steel, 6 is a gasket made of polypropylene, and 7 is a separator made of polyethylene.

In the cylindrical nonaqueous electrolyte secondary battery 10' shown in fig. 2 and 3, 11 is a negative electrode, 12 is a negative electrode current collector, 13 is a positive electrode, 14 is a positive electrode current collector, 15 is the nonaqueous electrolyte of the present invention, 16 is a separator, 17 is a positive electrode terminal, 18 is a negative electrode terminal, 19 is a negative electrode, 20 is a negative electrode lead, 21 is a positive electrode, 22 is a positive electrode lead, 23 is a case, 24 is an insulating plate, 25 is a gasket, 26 is a safety valve, and 27 is a PTC element.

Examples

The present invention will be specifically described below with reference to examples and comparative examples, which do not limit the scope of the present invention. In the examples, "parts" or "%" are by mass unless otherwise specified.

All the operations in the examples were carried out in a drying chamber, and the moisture was measured using a Karl Fischer moisture meter.

In the electrolyte a: LiPF is dissolved at a concentration of 0.8mol/L in a mixed solvent containing 30 vol% of ethylene carbonate, 40 vol% of ethylmethyl carbonate, and 30 vol% of dimethyl carbonate₆LiN (SO) was dissolved at a concentration of 0.2mol/L₂CF₃)₂. Then, in order to reduce the moisture content of the electrolyte, dry nitrogen gas was blown into the electrolyte at 20 ℃ for 24 hours at 3L/min through a glass capillary tube, and further, the electrolyte was heated to 70 ℃ and dry nitrogen gas was blown at 3L/min according to the method described in WO 99/34471. The moisture content of the electrolyte a obtained in this manner was 1.3 mass ppm.

In the electrolyte B: in a mixed solvent containing 50 vol% of ethylene carbonate and 50 vol% of diethyl carbonate, LiBF was dissolved at a concentration of 1.0mol/L₄An electrolyte solution is prepared. Thereafter, the same operation as in the case of the electrolyte solution a was performed, thereby obtaining an electrolyte solution B. The moisture content of the electrolyte B was 1.8 mass ppm.

To the electrolyte solution a or the electrolyte solution B, the following silicon compound and silyl ester compound were added according to the formulation shown in table 1, and the water content was adjusted to prepare electrolyte solutions of examples 1 to 25 and comparative examples 1 to 18. The adjustment of the moisture content is performed by blending the electrolyte solution in which the moisture content is reduced and the electrolyte solution before the moisture content is reduced.

< silicon Compound >

A1: trimethylphenylsilane

A2: 1, 4-bis (trimethylsilyl) benzene

A3: dimethyl diphenylsilane

A' 1: triethylsilane

A' 2: 1,1,3,3, 3-hexamethyldisilazane

A' 3: dimethoxydimethylsilane

< silyl ester Compound >

B1: trimethylsilyl methacrylate

B2: succinic acid bis (trimethylsilyl) ester

B3: fumaric acid bis (trimethylsilyl) ester

B4: 2, 2' -Thiodiacetic acid bis (trimethylsilyl) ester

B5: 2, 5-Thiophenedicarboxylic acid bis (trimethylsilyl) ester

B6: benzene-1, 2, 4-tricarboxylic acid tris (trimethylsilyl) ester

B7: bis (trimethylsilyl) sulfate

B8: benzenesulfonic acid trimethylsilyl ester

B9: phosphoric acid tris (trimethylsilyl) ester

B10: phosphorous acid tris (trimethylsilyl) ester

B11: boric acid tris (trimethylsilyl) ester

[ storage stability test ]

The storage stability of the electrolyte solution was evaluated by measuring the residual rate of the silyl ester compound by the following method. It can be said that the higher the survival rate, the higher the storage stability.

[ storage stability test method ]

The electrolyte was placed in a stainless steel container under an argon atmosphere, sealed, and stored in a thermostatic bath at 45 ℃ to obtain an electrolyte after 3 weeks of storage.

Comprising silyl phosphate compounds or phosphorous acidElectrolytic solution passing measurement of silyl ester Compound³¹P-NMR to calculate the residual ratio, and the electrolyte solution containing the carboxylic acid silyl ester compound, the sulfuric acid silyl ester compound, and the sulfonic acid silyl ester compound was measured¹The residual ratio was calculated by H-NMR.

[ utilization of³¹Method of P-NMR

The electrolyte solution to which triphenylphosphine was added as a reference substance was measured under the following conditions³¹P-NMR was carried out to determine the ratio of the area of the peak derived from the phosphosilyl ester compound or the phosphosilyl ester compound to the area of the peak derived from the reference substance. The ratio (%) of the area of the peak after the storage test to the area of the peak before the storage test was defined as the residual ratio.

A measuring device: nuclear magnetic resonance device, model number ECA-600, manufactured by Nippon electronic Co., Ltd

Solvent: deuterated chloroform

Reference substance: triphenylphosphine (-6.0ppm)

[ utilization of¹Method of H-NMR

The electrolyte solution was measured under the following conditions¹H-NMR was carried out to determine the ratio of the area of the peak derived from the trimethylsilyl group of the silyl ester compound to the area of the peak derived from the ethylene carbonate in the solvent. The ratio (%) of the area of the peak after the storage test to the area of the peak before the storage test was defined as the residual ratio.

Solvent: deuterated chloroform

Reference substance: ethylene carbonate (4.58ppm)

< addition of test method >

[ Charge-discharge cycle test ]

In the examples and comparative examples, nonaqueous electrolyte secondary batteries (lithium ion secondary batteries) were produced according to the following production steps.

[ manufacture of Positive electrode ]

LiNi was added as an active material in an amount of 90 parts by mass_1/3Co_1/3Mn_1/3O₂(NCM₁₁₁: manufactured by japan chemical industry), 5 parts by mass of acetylene black (AB: denka, product), and 5 parts by mass of polyvinylidene fluoride (PVDF: KUREHA) was dispersed in 120 parts by mass of N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The slurry was applied to an aluminum current collector, dried, and then pressure-molded. Then, the electrode was cut into a predetermined size to prepare a disk-shaped positive electrode. The electrode capacity of the positive electrode was set to 2.5mAh/cm²。

[ production of cathode ]

96 parts by mass of artificial graphite (MAG, manufactured by Hitachi chemical Co., Ltd.) as an active material, 1 part by mass of acetylene black (AB, manufactured by Denka) as a conductive assistant, 1.5 parts by mass of a 40% by mass aqueous dispersion of SBR (manufactured by Zeon, Japan) as a binder, and 1.5 parts by mass of sodium carboxymethylcellulose (CMC, manufactured by Daicel FineChem) as a thickener were dispersed in 120 parts by mass of water to prepare a slurry. The slurry was applied to a copper current collector, dried, and then pressure-molded. Then, the electrode was cut into a predetermined size to prepare a disk-shaped negative electrode. The electrode capacity of the negative electrode was set to 2.8mAh/cm²。

[ Assembly of Battery ]

The obtained disk-shaped positive electrode and disk-shaped negative electrode were held in a case with a microporous film made of polyethylene having a thickness of 25 μm serving as a separator interposed therebetween. Then, each nonaqueous electrolyte prepared previously was poured into a case, and the case was sealed and sealed to prepare nonaqueous electrolyte secondary batteries of examples and comparative examples (

Coin type with a thickness of 3.2 mm).

[ Charge-discharge cycle test method ]

The nonaqueous electrolyte secondary battery was placed in a thermostatic bath at 25 ℃ and charged at a current of 0.5mA/cm²(current value corresponding to 0.2C) was charged at constant current until 4.2V and discharged at a current of 0.5mA/cm²(current value corresponding to 0.2C) constant current dischargeThe operation was performed 5 times until the voltage reached 3.0V. Thereafter, the sample was transferred to a constant temperature bath at 45 ℃ and charged at a charging current of 2.5mA/cm²(current value corresponding to 1C) was charged at constant current until 4.2V and discharged at a current of 2.5mA/cm²(corresponding to a current value of 1C) the operation of the cycle until the constant current discharge was completed to 3.0V was performed 100 times. As shown in the following formula, the discharge capacity maintenance rate (%) was determined at a rate of the discharge capacity after 100 cycles of the test with the initial discharge capacity at 1C being 100.

The discharge capacity maintenance rate (%) (discharge capacity at 100 th cycle (1C))/(discharge capacity at 1 st cycle (1C)) ] × 100

TABLE 1

The number in () in the table is the content (unit: mass%) of the silicon compound or silyl ester compound in the electrolytic solution.

From the results of the storage stability test, the residual rate of the silyl ester compound was high in the electrolyte solution containing the phenylsilane compound represented by the general formula (1) of the present invention, but the residual rate was decreased in comparative examples 11 and 16 in which the water content exceeded 1000 ppm.

When the storage stability test and the charge-discharge cycle test were compared, it was found that the discharge capacity maintaining rate was high in the battery using the electrolyte solution having a high silyl ester compound remaining rate in the storage stability test, and the discharge capacity was maintained as the silyl ester compound remained.

Industrial applicability

According to the present invention, in the nonaqueous electrolytic solution obtained by dissolving the lithium salt containing a fluorine atom and the silyl ester compound in the organic solvent, even when some moisture is present, the decomposition of the silyl ester compound can be suppressed, and the storage stability can be improved.

Claims

1. A method for suppressing decomposition of a silyl ester compound, which is a method for suppressing decomposition of a silyl ester compound in a nonaqueous electrolytic solution containing a lithium salt containing a fluorine atom, a silyl ester compound selected from the group consisting of a carboxylic acid silyl ester compound, a sulfuric acid silyl ester compound, a sulfonic acid silyl ester compound, a phosphorous acid silyl ester compound, a phosphoric acid silyl ester compound and a boric acid silyl ester compound, and an organic solvent, wherein,

a phenylsilane compound represented by the following general formula (1) is mixed in the nonaqueous electrolytic solution in an amount of 0.1-10 mass%, and the water content of the nonaqueous electrolytic solution is set to be less than 1000 mass ppm,

in the formula, R¹、R²、R³、R⁴And R⁵Each independently represents a hydrogen atom, a halogen atom, a nitrile group, a nitro group, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, an oxyalkyl group having 1 to 12 carbon atoms, an acyl group having 1 to 12 carbon atoms or-SiR⁸R⁹R¹⁰A group represented by, R⁶、R⁷、R⁸、R⁹And R¹⁰Independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, and X¹Represents a hydrocarbon group having a valence of m, and m represents a number of 1 to 3.

2. The method for suppressing decomposition of a silyl ester compound according to claim 1, wherein said lithium salt containing a fluorine atom is selected from the group consisting of LiPF₆、LiBF₄、Li₂SiF₆、LiSbF₆、LiN(SO₂F)₂、LiOSO₂CF₃、LiN(SO₂CF₃)₂And LiN (SO)₂CF₂CF₃)₂1 or 2 or more of the group.

3. The method for suppressing decomposition of a silyl ester compound according to claim 1 or 2, wherein the silyl ester carboxylate compound is a compound represented by the following general formula (2),

in the formula, R¹¹、R¹²And R¹³Independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, and X²Represents a direct bond or a group having a valence of n, and n represents a number of 1 to 4.

4. The method for suppressing decomposition of a silyl ester compound according to claim 1 or 2, wherein the silyl sulfate compound and the silyl sulfonate compound are compounds represented by the following general formula (3),

in the formula, R¹⁴、R¹⁵、R¹⁶And R¹⁷Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, and p represents a number of 0 or 1.

5. The method for suppressing decomposition of a silyl ester compound according to claim 1 or 2, wherein the silyl ester phosphite compound and the silyl ester phosphate compound are compounds represented by the following general formula (4),

in the formula, R¹⁸、R¹⁹、R²⁰、R²¹、R²²、R²³、R²⁴、R²⁵And R²⁶Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms, and q represents a number of 0 or 1.

6. The method for suppressing decomposition of a silyl ester compound according to claim 1 or 2, wherein the silyl ester borate compound is a compound represented by the following general formula (5),

in the formula, R²⁷、R²⁸、R²⁹、R³⁰、R³¹、R³²、R³³、R³⁴And R³⁵Each independently represents an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms or an aralkyl group having 7 to 12 carbon atoms.

7. The method for suppressing decomposition of a silyl ester compound according to any one of claims 1 to 6, wherein the amount of water in the nonaqueous electrolytic solution is 5 ppm by mass or more.