JP2011171282A - Nonaqueous electrolyte and electrochemical element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte which can improve low-temperature cycle characteristics, and an electrochemical element using the same. <P>SOLUTION: In the nonaqueous electrolyte, an electrolyte salt is dissolved in a nonaqueous solvent. The electrochemical element and the nonaqueous solution each includes therein: 0.1-5 mass% of a vinyl ester derivative expressed by the following general formula (I); and 0.1-5 mass% of a compound which has S-O bond (A) and S=O bond (B) in the structure, and in which the total number of (A) and (B) is 3. In the formula, R<SP>1</SP>denotes a 1-4C alkyl group or a hydrogen atom. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolytic solution capable of improving low-temperature cycle characteristics and an electrochemical device using the same.

In recent years, electrochemical devices, particularly lithium secondary batteries, have been widely used as power sources for electronic devices such as mobile phones and laptop computers, and for power sources for electric vehicles and power storage. Since these electronic devices and automobiles are likely to be used in a wide temperature range such as a high temperature in midsummer or a low temperature in extremely cold, there is a demand for improving the cycle characteristics in a well-balanced manner over a wide temperature range.
The lithium secondary battery is mainly composed of a positive electrode and a negative electrode containing a material capable of occluding and releasing lithium, a non-aqueous electrolyte composed of a lithium salt and a non-aqueous solvent, and the non-aqueous solvent includes ethylene carbonate (EC), Carbonates such as propylene carbonate (PC) are used.
In addition, as the negative electrode, metal lithium, metal compounds that can occlude and release lithium (metal simple substance, oxide, alloy with lithium, etc.) and carbon materials are known, and in particular, lithium can be occluded and released. Lithium secondary batteries using carbon materials such as coke, artificial graphite and natural graphite have been widely put into practical use.

For example, a lithium secondary battery using a highly crystallized carbon material such as natural graphite or artificial graphite as a negative electrode material is a decomposition product generated by reductive decomposition of a solvent in a non-aqueous electrolyte on the negative electrode surface during charging. It is known that the gas can interfere with the desired electrochemical reaction of the battery, resulting in poor cycle characteristics. In addition, if the decomposition product of the nonaqueous solvent accumulates, lithium cannot be smoothly occluded and released from the negative electrode, and the cycle characteristics particularly at low temperatures are likely to deteriorate.
Furthermore, lithium secondary batteries using lithium metal, alloys thereof, simple metals such as tin or silicon, and oxides as negative electrode materials have high initial capacities, but fine powders progress during the cycle. In comparison, it is known that reductive decomposition of a non-aqueous solvent occurs at an accelerated rate, and battery performance such as battery capacity and cycle characteristics is greatly reduced. Further, if these anode materials are pulverized or a decomposition product of a non-aqueous solvent accumulates, lithium cannot be smoothly occluded and released, and cycle characteristics at low temperatures are likely to deteriorate.
On the other hand, a lithium secondary battery using, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFePO ₄ as the positive electrode is not separated from the positive electrode material when the non-aqueous solvent in the non-aqueous electrolyte is charged. Degradation products and gases generated by partial oxidative decomposition at the interface with the water electrolyte inhibit the desired electrochemical reaction of the battery, which also causes deterioration in battery performance such as cycle characteristics. It has been known.

As described above, the battery performance is degraded by inhibiting the migration of lithium ions or swelling of the battery due to decomposition products or gas generated when the nonaqueous electrolyte is decomposed on the positive electrode or the negative electrode. In spite of such a situation, electronic devices equipped with lithium secondary batteries are becoming more and more multifunctional and power consumption is increasing. As a result, the capacity of lithium secondary batteries has been increasing, and the volume occupied by non-aqueous electrolyte in the battery has become smaller, such as increasing the electrode density and reducing the useless space volume in the battery. . Therefore, the performance of the battery at low temperatures is likely to deteriorate with a slight decomposition of the non-aqueous electrolyte.
Patent Document 1 discloses that a cycle characteristic at 20 ° C. can be improved in a lithium ion secondary battery in which vinyl acetate is added to a nonaqueous electrolytic solution. Patent Document 2 discloses that the initial charge / discharge efficiency and cycle characteristics can be improved in a lithium ion secondary battery in which ethylene sulfite is added to the electrolyte.

Japanese Patent Laid-Open No. 11-273724 JP 2002-270230 A

  An object of this invention is to provide the nonaqueous electrolyte which can improve a low-temperature cycling characteristic, and an electrochemical element using the same.

The present inventors have examined in detail the performance of the above-described prior art non-aqueous electrolyte. As a result, the non-aqueous electrolyte of the above-mentioned patent document did not have a significant effect on the low temperature cycle characteristics.
Therefore, the present inventors have a vinyl ester derivative and a compound having an S—O bond (A) and an S═O bond (B) in the structure, and the total number of (A) and (B) is 3. It was found that the low-temperature cycle characteristics can be improved by adding to the non-aqueous electrolyte in combination, and the present invention has been achieved.

That is, the present invention provides the following (1) to (2).
(1) In a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, the vinyl ester derivative represented by the following general formula (I) is contained in an amount of 0.1 to 5% by mass with respect to the non-aqueous electrolyte. Further, 0.1 to 5% by mass of a compound having S—O bond (A) and S═O bond (B) in the structure and the total number of (A) and (B) being 3 is contained. A non-aqueous electrolyte characterized by:

（式中、Ｒ^１は炭素数１〜４のアルキル基または水素原子を示す。）

(In the formula, R ¹ represents an alkyl group having 1 to 4 carbon atoms or a hydrogen atom.)

(2) An electrochemical element including a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a nonaqueous solvent, and represented by the general formula (I) with respect to the nonaqueous electrolyte solution It contains 0.1 to 5% by mass of a vinyl ester derivative, further has an S—O bond (A) and an S═O bond (B) in the structure, and the total number of (A) and (B) is 3 An electrochemical device comprising 0.1 to 5% by mass of a compound that is:

  ADVANTAGE OF THE INVENTION According to this invention, the non-aqueous electrolyte which can improve a low-temperature cycle characteristic, and an electrochemical element using the same can be provided.

  The present invention relates to a non-aqueous electrolyte and an electrochemical device using the same.

[Non-aqueous electrolyte]
The non-aqueous electrolyte solution of the present invention is a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, wherein the vinyl ester derivative represented by the general formula (I) is added to the non-aqueous electrolyte solution in an amount of 0. A compound containing 1 to 5% by mass, further having an S—O bond (A) and an S═O bond (B) in the structure, and the total number of (A) and (B) being 3 is 0.00. It is characterized by containing 1 to 5% by mass.

In the combination of a vinyl ester derivative of the present invention and a compound having an S—O bond (A) and an S═O bond (B) in the structure, and the total number of (A) and (B) is 3. The reason why the nonaqueous electrolytic solution containing each of them at a concentration of 0.1 to 5% by mass can greatly improve the low-temperature cycle characteristics is not necessarily clear, but is considered as follows.
Non-aqueous electrolysis in which a vinyl ester derivative or a compound having an S—O bond (A) and an S═O bond (B) in the structure and the total number of (A) and (B) is 3 is added alone. In the liquid, the additive is reduced on the negative electrode to form a protective film derived from the additive. This coating increases the resistance of the negative electrode, and Li is deposited on the negative electrode surface when the low temperature cycle is repeated. As a result, there has been a problem that the distance between the separator and the negative electrode is widened and the cycle characteristics are deteriorated.
However, by using a combination of a vinyl ester derivative and a compound having S—O bond (A) and S═O bond (B) in the structure and the total number of (A) and (B) is 3. The formed mixed film improves the adhesion between the negative electrode and the separator, so that the insertion and desorption of Li becomes smooth, the precipitation of Li is suppressed, and the low temperature cycle characteristics are improved. As a result, the present invention has been achieved. Further, among the compounds having S—O bond (A) and S═O bond (B) in the structure and the total number of (A) and (B) is 3, a cyclic skeleton or a carbon-carbon triplet. It has been found that the above effect is further enhanced when a bond is included in the structure.

  The vinyl ester derivative contained in the nonaqueous electrolytic solution of the present invention is preferably one represented by the following general formula (I).

（式中、Ｒ^１は炭素数１〜４のアルキル基または水素原子を示す。）

(In the formula, R ¹ represents an alkyl group having 1 to 4 carbon atoms or a hydrogen atom.)

In the general formula (I), the substituent R ¹ is preferably an alkyl group having 1 to 4 carbon atoms, and the alkyl group having 1 to 4 carbon atoms is preferably a methyl group, an ethyl group, a propyl group, or a butyl group. .
Among these, from the viewpoint of improving low-temperature cycle characteristics, R ¹ is more preferably a methyl group or an ethyl group, and particularly preferably a methyl group.

  Specific examples of the compound represented by the general formula (I) include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl valerate. Among the above compounds, vinyl acetate and vinyl propionate are more preferable, and vinyl acetate is particularly preferable from the viewpoint of improving low-temperature cycle characteristics.

  The compound having an S—O bond (A) and an S═O bond (B) in the structure contained in the nonaqueous electrolytic solution of the present invention, and the total number of (A) and (B) is 3, Those represented by the following general formulas (II) to (IV) are preferred.

（式中、Ｒ²及びＲ³は炭素数１〜４のアルキル基または水素原子を示す。Ｒ²及びＲ³は互いに結合して環を形成しても良い。）

(In the formula, R ² and R ³ represent an alkyl group having 1 to 4 carbon atoms or a hydrogen atom. R ² and R ³ may combine with each other to form a ring.)

（式中、Ｒ^４は炭素数３〜６の直鎖又は分枝のアルキレン基を示す。）

(In the formula, R ⁴ represents a linear or branched alkylene group having 3 to 6 carbon atoms.)

（式中、Ｒ^５は炭素数１〜４のアルキル基を示し、Ｒ^６は炭素数１〜３の直鎖又は分枝のアルキレン基を示す。）

(In the formula, R ⁵ represents an alkyl group having 1 to 4 carbon atoms, and R ⁶ represents a linear or branched alkylene group having 1 to 3 carbon atoms.)

In the general formula (II), the substituents R ² and R ³ are preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and the alkyl group having 1 to 4 carbon atoms may be a methyl group, an ethyl group, or propyl group. Group and butyl group are preferred.

  Specific examples of the compound represented by the general formula (II) include ethylene sulfite, propylene sulfite, 1-ethylethylene sulfite, 1,2-dimethylethylene sulfite, 1,2-cyclohexanediol cyclic sulfite. Fight is preferred. Among the above compounds, ethylene sulfite and 1,2-cyclohexanediol cyclic sulfite are more preferable, and ethylene sulfite is particularly preferable from the viewpoint of improving low-temperature cycle characteristics.

In the general formula (III), the substituent R ⁴ is preferably a linear or branched alkylene group having 3 to 6 carbon atoms, and the linear or branched alkylene group having 3 to 6 carbon atoms is propylene. Group, butylene group, pentene group, hexene group, 2-methylpropane-1,3-diyl group, butane-1,3-diyl group and butane-2,4-diyl group are preferable.
Among these, from the viewpoint of improving low-temperature cycle characteristics, a propylene group and a butylene group are more preferable, and a propylene group is particularly preferable.

Specific examples of the compound represented by the general formula (III) include 1,3-propane sultone, 1,4-butane sultone, 1,5-pentane sultone, 1-methyl-1,3-propane sultone, 2- Methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1,2-dimethyl-1,3-propane sultone, 2,3-dimethyl-1,3-propane sultone, 1,3- Dimethyl-1,3-propane sultone is preferred. Among these compounds, 1,3-propane sultone and 1,4-butane sultone are more preferable, and 1,3-propane sultone is particularly preferable from the viewpoint of improving low-temperature cycle characteristics.

In the general formula (IV), the substituent R ⁵ is preferably an alkyl group having 1 to 4 carbon atoms, and the alkyl group having 1 to 4 carbon atoms is preferably a methyl group, an ethyl group, a propyl group, or a butyl group. .
Among these, from the viewpoint of improving low-temperature cycle characteristics, a methyl group and an ethyl group are more preferable, and a methyl group is particularly preferable.

In the general formula (IV), the substituent R ⁶ is preferably a linear or branched alkylene group having 1 to 3 carbon atoms, and the linear or branched alkylene group having 1 to 3 carbon atoms is methylene. Group, ethylene group, propylene group, —C (CH ₃ ) ₂ —, —CH (CH ₃ ) —, —C (CH ₃ ) ₂ CH ₂ —, and —CH (CH ₃ ) CH ₂ — are preferable.
Among these, from the viewpoint of improving low-temperature cycle characteristics, a methylene group and an ethylene group are more preferable, and a methylene group is particularly preferable.
In this specification, the alkylene group is used as a concept including a methylene group.

Specific examples of the compound represented by the general formula (IV) include 2-propynyl methanesulfonate, 2-propynyl ethanesulfonate, 2-propynyl propanesulfonate, 2-butynyl methanesulfonate, and 2-methane sulfonate. Pentynyl, 1,1-dimethyl-2-propynyl methanesulfonate, and 1-methyl-2-propynyl methanesulfonate are preferred. Among the above compounds, 2-propynyl methanesulfonate and 1,1-dimethyl-2-propynyl methanesulfonate are more preferable, and 2-propynyl methanesulfonate is particularly preferable from the viewpoint of improving low-temperature cycle characteristics.

In the non-aqueous electrolyte of the present invention, the content of the vinyl ester derivative represented by the general formula (I) contained in the non-aqueous electrolyte is 0.1 to 5% by mass with respect to the non-aqueous electrolyte. is there. When the content exceeds 5% by mass, a film is excessively formed on the electrode, so that the low-temperature cycle characteristics may be deteriorated. When the content is less than 0.1% by mass, the film is not sufficiently formed. In some cases, the effect of improving the low-temperature cycle characteristics cannot be obtained. The content is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 1% by mass or more, and the upper limit thereof is preferably 5% by mass or less, based on the non-aqueous electrolyte. 3 mass% or less is more preferable, and 2 mass% or less is still more preferable.
The content of the compound having S—O bond (A) and S═O bond (B) in the structure and the total number of (A) and (B) being 3 is It is 0.1-5 mass%. When the content exceeds 5% by mass, a film is excessively formed on the electrode, so that the low-temperature cycle characteristics may be deteriorated. When the content is less than 0.1% by mass, the film is not sufficiently formed. In some cases, the effect of improving the low-temperature cycle characteristics cannot be obtained. The content is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 1% by mass or more, and the upper limit thereof is preferably 5% by mass or less, based on the non-aqueous electrolyte. 3 mass% or less is more preferable, and 2 mass% or less is still more preferable. These compounds may be used alone, and when two or more compounds are used in combination, the low temperature cycle characteristics are further improved, which is more preferable.
In the nonaqueous electrolytic solution of the present invention, the vinyl ester derivative represented by the general formula (I) and the structure have S—O bond (A) and S═O bond (B), and (A) The low temperature cycle characteristics are improved by adding a combination of compounds in which the total number of (B) is 3, but the low temperature cycle characteristics are improved by combining the following non-aqueous solvent, electrolyte salt, and other additives. It produces a unique effect of synergistic improvement. The reason is not clear, but it is considered that a mixed film having high ion conductivity containing these non-aqueous solvent, electrolyte salt, and other constituent elements of additives is formed.

[Nonaqueous solvent]
Examples of the nonaqueous solvent used in the nonaqueous electrolytic solution of the present invention include cyclic carbonates, chain carbonates, chain esters, ethers, amides, phosphate esters, sulfones, lactones, and nitriles. , S═O bond-containing compounds other than compounds having S—O bond (A) and S═O bond (B) in the structure, and the total number of (A) and (B) is 3. It is done.
Cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), 4-fluoro-1,3-dioxolan-2-one (FEC), trans or cis-4,5-difluoro -1,3-dioxolan-2-one (hereinafter collectively referred to as “DFEC”), vinylene carbonate (VC), vinyl ethylene carbonate (VEC) and the like. Among these, inclusion of PC is more preferable because the low-temperature cycle characteristics are improved.

These solvents may be used alone, and when used in combination of two or more, the low-temperature cycle characteristics are further improved, and three or more are particularly preferable. Preferred combinations of these cyclic carbonates include EC and PC, EC and VC, PC and VC, FEC and VC, FEC and EC, FEC and PC, FEC and DFEC, DFEC and EC, DFEC and PC, DFEC and VC , DFEC and VEC, EC and PC and VC, EC and FEC and PC, EC and FEC and VC, EC and VC and VEC, FEC and PC and VC, DFEC and EC and VC, DFEC and PC and VC, FEC and EC And PC and VC, DFEC and EC, PC, and VC. Of the above combinations, more preferred are combinations of EC and PC, FEC and PC, DFEC and PC, EC and FEC and PC, and the like.
Although content in particular of cyclic carbonate is not restrict | limited, It is preferable to use in the range of 10 volume%-40 volume% with respect to the total volume of a nonaqueous solvent. If the content is less than 10% by volume, the conductivity of the non-aqueous electrolyte decreases, and the low-temperature cycle characteristics tend to decrease. If the content exceeds 40% by volume, the viscosity of the non-aqueous electrolyte increases and the low-temperature cycle characteristics. The above-mentioned range is preferable since there is a tendency to decrease.

Examples of chain carbonates include asymmetric chain carbonates such as methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, and ethyl propyl carbonate, dimethyl carbonate (DMC), and diethyl carbonate. (DEC), symmetric chain carbonates such as dipropyl carbonate and dibutyl carbonate.
Among them, it is preferable to include a chain carbonate having a methyl group, more preferably at least one of DMC, MEC, MPC, and MIPC, and particularly preferably at least one of DMC and MEC. Furthermore, it is preferable that an asymmetric chain carbonate is contained, and it is more preferable to use an asymmetric chain carbonate and a symmetric chain carbonate in combination. Moreover, it is preferable that the ratio of the asymmetric linear carbonate contained in a linear carbonate is 50 volume% or more.
These chain carbonates may be used alone or in combination of two or more.
It is preferable that the chain carbonate has a combination or composition range because the low-temperature cycle characteristics tend to be improved.
The content of the chain carbonate is not particularly limited, but it is preferably used in the range of 60 to 90% by volume with respect to the total volume of the nonaqueous solvent. If the content is less than 60% by volume, the viscosity of the electrolytic solution increases, and if it exceeds 90% by volume, the electrical conductivity of the electrolytic solution may decrease and the electrochemical characteristics such as load characteristics may decrease. A range is preferable.
The ratio of the cyclic carbonates to the chain carbonates is preferably 10:90 to 40:60, preferably 15:85 to 35:65, from the viewpoint of improving low-temperature cycle characteristics. Is more preferable, and 20:80 to 30:70 is particularly preferable.

  Other nonaqueous solvents include chain esters such as methyl propionate, methyl pivalate, butyl pivalate, hexyl pivalate, octyl pivalate, dimethyl oxalate, ethyl methyl oxalate, diethyl oxalate, tetrahydrofuran, -Cyclic ethers such as methyltetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, etc. Chain ethers, amides such as dimethylformamide, phosphate esters such as trimethyl phosphate, tributyl phosphate, trioctyl phosphate, sulfones such as sulfolane, γ-butyrolactone, γ-valerolactone, α-angelica lactone Lactones such as acetonitrile, propionitri , Nitriles such as succinonitrile, glutaronitrile, adiponitrile, pimeonitrile, suberonitrile, azeronitrile, 1,2-ethanediol dimethanesulfonate, 1,2-propanediol dimethanesulfonate, 1,3-propanediol dimethanesulfonate 1,4-butanediol dimethanesulfonate, disulfonic acid ester compounds such as 1,5-pentanediol dimethanesulfonate, divinylsulfone, 1,2-bis (vinylsulfonyl) ethane, bis (2-vinylsulfonylethyl) ether S = O bond-containing compounds selected from vinyl sulfone compounds such as, chain carboxylic acid anhydrides such as acetic anhydride and propionic anhydride, cyclic such as succinic anhydride, maleic anhydride, glutaric anhydride and itaconic anhydride Mosquito Boronic anhydride, cyclohexylbenzene, fluorocyclohexylbenzene compound (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), tert-butylbenzene, tert-amylbenzene , Aromatic compounds having a branched alkyl group such as 1-fluoro-4-tert-butylbenzene, biphenyl, terphenyl (o-, m-, p-form), 1,2,3,4-tetrahydronaphthalene , Naphthalene, diphenyl ether, fluorobenzene, difluorobenzene (o-, m-, p-isomer), anisole, 2,4-difluoroanisole, partially hydrogenated terphenyl (1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl) 1,2-di E sulfonyl cyclohexane) aromatic compounds can be preferably used.

The disulfonate compound is a vinyl ester derivative and a compound having an S—O bond (A) and an S═O bond (B) in the structure, and the total number of (A) and (B) is 3. When used together, the adhesion between the negative electrode and the separator is further improved, and the low-temperature cycle characteristics can be further improved. Among these, 1,2-ethanediol dimethanesulfonate, 1,3-propanediol dimethanesulfonate, 1,4-butanediol dimethanesulfonate, and 1,5-pentanediol dimethanesulfonate are more preferable, and 1,5-pentane. Diol dimethanesulfonate is particularly preferred.
When the content of the disulfonic acid ester compound exceeds 5% by mass, the low temperature cycle characteristics may be deteriorated, and when the content is less than 0.1% by mass, the effect of improving the low temperature cycle characteristics is not sufficiently obtained. There is. Therefore, the lower limit of the content of the disulfonic acid ester compound is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 1% by mass or more with respect to the nonaqueous electrolytic solution. Moreover, the upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 2% by mass or less.

The dinitrile compound is used in combination with a vinyl ester derivative and a compound having an S—O bond (A) and an S═O bond (B) in the structure, and the total number of (A) and (B) is 3. Then, the adhesiveness of a negative electrode and a separator improves more, and a low temperature cycling characteristic can be improved further. Among these, succinonitrile, glutaronitrile, adiponitrile, and pimelonitrile are more preferable, and adiponitrile and pimelonitrile are particularly preferable.
If the content of the dinitrile compound exceeds 5% by mass, the low temperature cycle characteristics may be deteriorated, and if it is less than 0.1% by mass, the effect of improving the low temperature cycle characteristics may not be sufficiently obtained. . Therefore, the lower limit of the content of the dinitrile compound is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 1% by mass or more with respect to the nonaqueous electrolytic solution. Moreover, the upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 2% by mass or less.

The aromatic compound includes a vinyl ester derivative and a compound having an S—O bond (A) and an S═O bond (B) in the structure, and the total number of (A) and (B) is 3. When used in combination, the adhesion between the negative electrode and the separator is further improved, and the low-temperature cycle characteristics can be further improved. Among these, biphenyl, cyclohexylbenzene, 1,2,3,4-tetrahydronaphthalene and anisole are more preferable.
If the content of the aromatic compound exceeds 5% by mass, the low-temperature cycle characteristics may be deteriorated, and if it is less than 0.1% by mass, the effect of improving the low-temperature cycle characteristics may not be sufficiently obtained. is there. Therefore, the lower limit of the content of the aromatic compound is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 1% by mass or more with respect to the nonaqueous electrolytic solution. Moreover, the upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 2% by mass or less.

The above non-aqueous solvents are usually used as a mixture in order to achieve appropriate physical properties. The combinations include, for example, combinations of cyclic carbonates and chain carbonates, combinations of cyclic carbonates, chain carbonates and lactones, combinations of cyclic carbonates, chain carbonates and ethers, and cyclic carbonates. Examples include combinations of chain carbonates and chain esters, combinations of cyclic carbonates, chain carbonates, and nitriles.
Among these, it is preferable to use a non-aqueous solvent in which at least a cyclic carbonate and a chain carbonate are combined because the low-temperature cycle characteristics are improved. The ratio between the cyclic carbonate and the chain carbonate is not particularly limited, but the cyclic carbonate: chain carbonate (volume ratio) is preferably 10:90 to 40:60, and 15:85 to 35:65. Is more preferable, and 20:80 to 30:70 is still more preferable.

[Electrolyte salt]
Examples of the electrolyte used in the present invention include Li salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ( _{SO 2 CF 3) 3, LiPF} 4 (CF 3) 2, LiPF 3 (C 2 F 5) 3, LiPF 3 (CF 3) 3, LiPF 3 (iso-C 3 F 7) 3, LiPF 5 (iso- Lithium salts containing a chain-like fluorinated alkyl group such as C ₃ F ₇ ) and cyclic fluorination such as (CF ₂ ) ₂ (SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ NLi Lithium salt containing an alkylene chain, lithium salt having an oxalate complex such as lithium bis [oxalate-O, O ′] lithium borate or difluoro [oxalate-O, O ′] lithium borate as an anion Is mentioned. Among these, particularly preferable electrolyte salts are LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO ₂ C ₂ F ₅ ) ₂ . These electrolyte salts can be used singly or in combination of two or more.

  The concentration used by dissolving all the electrolyte salts is usually preferably 0.3 M or more, more preferably 0.5 M or more, and even more preferably 0.7 M or more with respect to the non-aqueous solvent. Moreover, the upper limit is preferably 2.5 M or less, more preferably 2.0 M or less, and even more preferably 1.5 M or less.

[Production of non-aqueous electrolyte]
In the non-aqueous electrolyte of the present invention, for example, the above-mentioned non-aqueous solvent is mixed, and the vinyl salt derivative represented by the above general formula (I) is added to the above-described electrolyte salt and the non-aqueous electrolyte in an amount of 0. 1 to 5% by mass, a compound having an S—O bond (A) and an S═O bond (B) in the structure, and the total number of (A) and (B) is 3, It can be obtained by dissolving 5% by mass.
At this time, it is preferable that the compound added to the non-aqueous solvent and the non-aqueous electrolyte to be used is one that is purified in advance and has as few impurities as possible within a range that does not significantly reduce the productivity.

The nonaqueous electrolytic solution of the present invention can be used for a lithium primary battery and a lithium secondary battery. Furthermore, the non-aqueous electrolyte of the present invention can also be used as an electrolyte for electric double layer capacitors and hybrid capacitors. Among them, it is most suitable to use for a lithium secondary battery.

[First electrochemical element (lithium battery)]
The lithium battery of the present invention is a generic term for a lithium primary battery and a lithium secondary battery. The lithium battery of the present invention comprises the nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a nonaqueous solvent. Components other than the non-aqueous electrolyte, such as a positive electrode and a negative electrode, can be used without particular limitation.
For example, as a positive electrode active material for a lithium secondary battery, a composite metal oxide with lithium containing at least one of cobalt, manganese, and nickel is used. These positive electrode active materials can be used singly or in combination of two or more.
Examples of such a lithium composite metal oxide include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <1), LiCo _1/3 Ni _1/3. Examples thereof include Mn _1/3 O ₂ , LiNi _1/2 Mn _3/2 O ₄ , and LiCo _0.98 Mg _0.02 O ₂ . Moreover, LiCoO ₂ and LiMn ₂ O _4, LiCoO ₂ and LiNiO _2, may be used in combination as LiMn ₂ O ₄ and LiNiO _2.

In addition, in order to improve safety and cycle characteristics during overcharge, or to enable use at a charging potential of 4.3 V or higher, a part of the lithium composite metal oxide may be substituted with another element. . For example, a part of cobalt, manganese, nickel is replaced with at least one element such as Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, La, etc. , A part of O may be substituted with S or F, or a compound containing these other elements may be coated.
Among these, lithium composite metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ that can be used at a charged potential of the positive electrode in a fully charged state of 4.3 V or more on the basis of Li are preferable, and LiCo _1-x M _x O ₂ (where M is at least one element represented by Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, 0.001 ≦ x ≦ 0.05) ), LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _1/2 Mn _3/2 O ₄ and other lithium composite metal oxides usable at 4.4 V or higher are more preferable. When a lithium composite metal composite oxide having a high charge voltage is used, the effect of improving the low temperature cycle characteristics due to the reaction with the electrolyte during charging tends to be reduced, but the lithium secondary battery according to the present invention has these battery characteristics. The decrease can be suppressed.

Furthermore, lithium-containing olivine-type phosphate can also be used as the positive electrode active material. In particular, a lithium-containing olivine-type phosphate containing at least one selected from iron, cobalt, nickel and manganese is preferable. Specific examples thereof include LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO _{4 and the} like.
Some of these lithium-containing olivine-type phosphates may be substituted with other elements, and some of iron, cobalt, nickel, and manganese are replaced with Co, Mn, Ni, Mg, Al, B, Ti, V, and Nb. , Cu, Zn, Mo, Ca, Sr, W and Zr can be substituted with one or more elements selected from these, or can be coated with a compound or carbon material containing these other elements. Among these, LiFePO ₄ or LiMnPO ₄ is preferable.
Moreover, lithium containing olivine type | mold phosphate can also be mixed with the said positive electrode active material, for example, and can be used.

As the positive electrode for lithium primary _{battery, CuO, Cu 2 O, Ag} 2 O, Ag 2 CrO 4, CuS, CuSO 4, TiO 2, TiS 2, SiO 2, SnO, V 2 O 5, V 6 O 12 , VO _x , Nb ₂ O ₅ , Bi ₂ O ₃ , Bi ₂ Pb ₂ O ₅ , Sb ₂ O ₃ , CrO ₃ , Cr ₂ O ₃ , MoO ₃ , WO ₃ , SeO ₂ , MnO ₂ , Mn ₂ O ₃ , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , CoO and other oxides of one or more metal elements or chalcogen compounds, sulfur such as SO ₂ and SOCl ₂ Examples thereof include a compound and fluorocarbon (fluorinated graphite) represented by the general formula (CF _x ) _n . Of these, MnO ₂ , V ₂ O ₅ , graphite fluoride and the like are preferable.

  The conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change. Examples thereof include graphite such as natural graphite (flaky graphite and the like) and artificial graphite, and carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black. Further, graphites and carbon blacks may be appropriately mixed and used. 1-10 mass% is preferable and, as for the addition amount to the positive mix of a electrically conductive agent, 2-5 mass% is especially preferable.

The positive electrode is composed of a conductive agent such as acetylene black and carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), acrylonitrile and butadiene. Mixing with a binder such as copolymer (NBR), carboxymethyl cellulose (CMC), ethylene propylene diene terpolymer, etc., and adding a high boiling point solvent such as 1-methyl-2-pyrrolidone to knead and mix Then, this positive electrode mixture was applied to a current collector aluminum foil, a stainless steel lath plate, etc., dried and pressure-molded, and then subjected to vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. It can be manufactured by heat treatment.
The density of the part except the collector of the positive electrode is usually at 1.5 g / cm ³ or more, for further increasing the capacity of the battery, it is preferably 2 g / cm ³ or more, more preferably, 3 g / cm ³ More preferably, it is 3.6 g / cm ³ or more. The upper limit is preferably 4 g / cm ³ or less.

As the negative electrode active material, a carbon material capable of inserting and extracting lithium is used. These negative electrode active materials can be used individually by 1 type or in combination of 2 or more types.
Examples of the carbon material capable of inserting and extracting lithium include graphitizable carbon, non-graphitizable carbon having a (002) plane spacing of 0.37 nm or more, and a (002) plane spacing of 0. A graphite of 34 nm or less is preferable.
Among these, it is more preferable to use a highly crystalline carbon material such as artificial graphite or natural graphite in terms of the ability to occlude and release lithium ions, and the plane spacing (d ₀₀₂ ) of the lattice plane ( ₀₀₂ ) is 0. It is particularly preferable to use a carbon material having a graphite-type crystal structure of 340 nm (nanometer) or less, particularly 0.335 to 0.337 nm.
A mechanical action such as compression force, friction force, shear force, etc. is repeatedly applied to artificial graphite particles having a massive structure in which a plurality of flat graphite fine particles are assembled or bonded non-parallel to each other, for example, scaly natural graphite particles, Graphite obtained from X-ray diffraction measurement of the negative electrode sheet when the density of the portion excluding the current collector of the negative electrode is pressed to a density of 1.5 g / cm ³ by using the spheroidized graphite particles When the ratio I (110) / I (004) of the peak intensity I (110) of the (110) plane and the peak intensity I (004) of the (004) plane is 0.01 or more, the low-temperature cycle characteristics are further improved. Therefore, it is preferably 0.05 or more, and more preferably 0.1 or more. Moreover, since it may process too much and crystallinity may fall and the discharge capacity of a battery may fall, 0.5 or less is preferable and 0.3 or less is still more preferable.
Further, it is preferable that the highly crystalline carbon material is coated with a low crystalline carbon material because the low-temperature cycle characteristics are improved. When a highly crystalline carbon material is used, it reacts with the non-aqueous electrolyte during charging and tends to lower the low-temperature cycle characteristics due to an increase in interface resistance, but the lithium secondary battery according to the present invention has a low-temperature cycle characteristic. It becomes good.

The negative electrode is kneaded using the same conductive agent, binder, and high-boiling solvent as in the production of the positive electrode, and then the negative electrode mixture is applied to the copper foil of the current collector. After being dried and pressure-molded, it can be produced by heat treatment under vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours.
The density of the portion excluding the current collector of the negative electrode is usually 1.1 g / cm ³ or more, and is preferably 1.5 g / cm ³ or more, particularly preferably 1.7 g in order to further increase the capacity of the battery. / Cm ³ or more. The upper limit is preferably 2 g / cm ³ or less.

The structure of the lithium battery is not particularly limited, and a coin-type battery, a cylindrical battery, a square battery, a laminated battery, or the like having a single-layer or multi-layer separator can be applied.
Although it does not restrict | limit especially as a separator for batteries, The porous film of monolayer or lamination | stacking of polyolefin, such as a polypropylene and polyethylene, a woven fabric, a nonwoven fabric, etc. can be used.

  The lithium secondary battery according to the present invention is excellent in low temperature cycle characteristics even when the end-of-charge voltage is 4.2 V or higher, particularly 4.3 V or higher, and also has good characteristics at 4.4 V or higher. The end-of-discharge voltage is usually 2.8 V or more, and further 2.5 V or more, but the lithium secondary battery in the present invention can be 2.0 V or more. Although it does not specifically limit about an electric current value, Usually, it uses in the range of 0.1-3C. Moreover, the lithium battery in this invention can be charged / discharged at -40-100 degreeC, Preferably it is -10-80 degreeC.

  In the present invention, as a countermeasure against an increase in the internal pressure of the lithium battery, a method of providing a safety valve on the battery lid or cutting a member such as a battery can or a gasket can be employed. Further, as a safety measure for preventing overcharge, the battery lid can be provided with a current interruption mechanism that senses the internal pressure of the battery and interrupts the current.

[Second electrochemical element (electric double layer capacitor)]
It is an electrochemical element that stores energy by using the electric double layer capacity at the electrolyte / electrode interface. An example of the present invention is an electric double layer capacitor. The most typical electrode active material used in this electrochemical device is activated carbon. Double layer capacity increases roughly in proportion to surface area.

[Third electrochemical element]
An electrochemical device that stores energy using electrode doping / dedoping reactions. Examples of the electrode active material used in this electrochemical element include metal oxides such as ruthenium oxide, iridium oxide, tungsten oxide, molybdenum oxide, and copper oxide, and π-conjugated polymers such as polyacene and polythiophene derivatives. Capacitors using these electrode active materials can store energy associated with electrode doping / dedoping reactions.

[Fourth electrochemical element (lithium ion capacitor)]
It is an electrochemical element that stores energy by utilizing lithium ion intercalation with a carbon material such as graphite as a negative electrode. It is called a lithium ion capacitor (LIC). Examples of the positive electrode include those using an electric double layer between an activated carbon electrode and an electrolytic solution, and those using a π-conjugated polymer electrode doping / dedoping reaction. The electrolyte contains at least a lithium salt such as LiPF ₆ .

Examples using the non-aqueous electrolyte of the present invention are shown below.
Examples 1-12, Comparative Examples 1-3
[Production of lithium ion secondary battery]
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ; 94% by mass, acetylene black (conductive agent); 3% by mass are mixed, and polyvinylidene fluoride (binder); In addition to the solution dissolved in -2-pyrrolidone, the mixture was mixed to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried and pressurized, punched out to a predetermined size, and a positive electrode sheet was produced. The density of the portion excluding the current collector of the positive electrode was 3.6 g / cm ³ . Further, 95% by mass of artificial graphite (d002 = 0.335 nm, negative electrode active material) coated with a low crystalline carbon material, and 5% by mass of polyvinylidene fluoride (binder) in advance are added with 1-methyl-2-pyrrolidone. The negative electrode mixture paste was prepared by adding to and mixing with the solution previously dissolved in the mixture. This negative electrode mixture paste was applied to one side of a copper foil (current collector), dried and pressurized, and punched into a predetermined size to produce a negative electrode sheet. The density of the portion excluding the current collector of the negative electrode was 1.5 g / cm ³ . Further, as a result of X-ray diffraction measurement using this electrode sheet, I (110) / I (004) was 0.1. And it laminated | stacked in order of the positive electrode sheet, the separator made from a microporous polyethylene film, and the negative electrode sheet, the nonaqueous electrolyte of the composition of Table 1 was added, and the 2032 type coin battery was produced.

[Evaluation of low-temperature cycle characteristics]
Using the coin battery produced by the above method, in a constant temperature bath at 25 ° C., charge at a constant current of 1C and a constant voltage for 3 hours to a final voltage of 4.2V, and then to a final voltage of 2.75V under a constant current of 1C. A precycle was performed by discharging.
Next, in a thermostat at 0 ° C., the battery was charged with a constant current and a constant voltage of 1 C to a final voltage of 4.2 V for 3 hours, and then discharged to a final voltage of 2.75 V under a constant current of 1 C. This was repeated until 50 cycles were reached. And the discharge capacity maintenance factor after 50 cycles was calculated | required with the following formula | equation.
Discharge capacity retention rate (%) = (discharge capacity after 50 cycles / discharge capacity after one cycle) × 100
Table 1 shows battery fabrication conditions and battery characteristics.

Example 13, Comparative Examples 4-5
A negative electrode sheet was prepared using Si (negative electrode active material) instead of the negative electrode active material used in Example 2 and Comparative Examples 1-2. Si: 80% by mass, acetylene black (conductive agent); 15% by mass are mixed and added to a solution in which 5% by mass is previously dissolved in 1-methyl-2-pyrrolidone. And mixed to prepare a negative electrode mixture paste. Except that this negative electrode mixture paste was applied onto a copper foil (current collector), dried and pressurized, punched out to a predetermined size, and a negative electrode sheet was prepared, Example 2, Comparative Examples 1 to A coin battery was prepared in the same manner as in No. 2, and the battery was evaluated. The results are shown in Table 2.

Example 14, Comparative Examples 6-7
A positive electrode sheet was produced using LiFePO ₄ (positive electrode active material) coated with amorphous carbon instead of the positive electrode active material used in Example 2 and Comparative Examples 1 and 2. LiFePO ₄ coated with amorphous carbon; 90% by mass, acetylene black (conductive agent); 5% by mass are mixed in advance and polyvinylidene fluoride (binder); 5% by mass in 1-methyl-2-pyrrolidone A positive electrode mixture paste was prepared by adding to the dissolved solution and mixing. This positive electrode mixture paste was applied onto an aluminum foil (current collector), dried, pressurized and punched to a predetermined size to produce a positive electrode sheet, and the end-of-charge voltage during battery evaluation was 3. A coin battery was manufactured and evaluated in the same manner as in Example 2 and Comparative Examples 1 and 2 except that 6 V and the discharge end voltage were set to 2.0 V. The results are shown in Table 3.

The lithium secondary batteries of Examples 1 to 12 are significantly improved in low-temperature cycle characteristics as compared with Comparative Example 1 in which vinyl acetate is added alone and Comparative Example 2 in which ethylene sulfite is added alone. is doing. Further, Comparative Example 3 in which a vinyl ester derivative and a compound having an S—O bond (A) and an S═O bond (B) in the structure and a total number of (A) and (B) is 4 were combined. Compared to the above, the low-temperature cycle characteristics are remarkably improved. From the above, the effect of the present invention is that the vinyl ester derivative and the structure have S—O bond (A) and S═O bond (B), and the total number of (A) and (B) is 3. It was found to be specific when certain compounds were combined.
Moreover, from the comparison between Example 13 and Comparative Examples 4 to 5, and from the comparison between Example 14 and Comparative Examples 6 to 7, when Si is used for the negative electrode, or when lithium-containing olivine iron phosphate is used for the positive electrode Has the same effect. Therefore, it is clear that the effect of the present invention is not an effect dependent on a specific positive electrode or negative electrode.

  Furthermore, the non-aqueous electrolyte of the present invention also has an effect of improving the low temperature load characteristics of the lithium primary battery.

  According to the present invention, if the nonaqueous electrolytic solution of the present invention is used, an electrochemical element having excellent low-temperature cycle characteristics can be obtained.

Claims (16)

In a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, the non-aqueous electrolyte solution contains 0.1 to 5% by mass of a vinyl ester derivative represented by the following general formula (I), and further has a structure. It contains 0.1 to 5% by mass of a compound having S—O bond (A) and S═O bond (B) in which the total number of (A) and (B) is 3. Non-aqueous electrolyte.

(In the formula, R ¹ represents an alkyl group having 1 to 4 carbon atoms or hydrogen.) The non-aqueous electrolyte according to claim 1, wherein the vinyl ester derivative is vinyl acetate. Compounds having the S—O bond (A) and the S═O bond (B) in the above structure and the total number of (A) and (B) being 3 are represented by the following general formulas (II) to (II): The non-aqueous electrolyte according to claim 1, which is represented by IV).

(In the formula, R ² and R ³ represent an alkyl group having 1 to 4 carbon atoms or a hydrogen atom. R ² and R ³ may combine with each other to form a ring.)

(In the formula, R ⁴ represents a linear or branched alkylene group having 3 to 6 carbon atoms.)

(In the formula, R ⁵ represents an alkyl group having 1 to 4 carbon atoms, and R ⁶ represents a linear or branched alkylene group having 1 to 3 carbon atoms.) Although represented by the general formula (II), it is selected from ethylene sulfite, propylene sulfite, 1-ethylethylene sulfite, 1,2-dimethylethylene sulfite, and 1,2-cyclohexanediol cyclic sulfite. The nonaqueous electrolytic solution according to claim 3, wherein the nonaqueous electrolytic solution is at least one kind. The non-aqueous electrolyte according to claim 3, wherein the compound represented by the general formula (III) is at least one selected from 1,3-propane sultone and 1,4-butane sultone. The non-aqueous electrolyte according to claim 3, wherein the compound represented by the general formula (IV) is 2-propynyl methanesulfonate. Further, at least one selected from 1,2-ethanediol dimethanesulfonate, 1,3-propanediol dimethanesulfonate, 1,4-butanediol dimethanesulfonate, and 1,5-pentanediol dimethanesulfonate is non-aqueous. The nonaqueous electrolytic solution according to claim 1, wherein the nonaqueous electrolytic solution is contained in an amount of 0.1 to 5 mass% with respect to the electrolytic solution. Furthermore, 0.1 to 5% by mass of at least one selected from biphenyl, o-terphenyl, cyclohexylbenzene, anisole, 1,2,3,4-tetrahydronaphthalene and naphthalene is contained in the nonaqueous electrolytic solution. The nonaqueous electrolytic solution according to claim 1, wherein Furthermore, 0.01-5 mass% is contained in a non-aqueous electrolyte at least 1 type chosen from a succinonitrile, glutaronitrile, adiponitrile, pimeonitrile, suberonitrile, and azeronitrile. Non-aqueous electrolyte. The nonaqueous electrolytic solution according to claim 1, wherein the nonaqueous solvent contains a cyclic carbonate and a chain carbonate. The non-aqueous electrolyte according to claim 10, wherein the chain carbonate has at least a methyl group.   The nonaqueous electrolytic solution according to claim 10, wherein the chain carbonate includes a symmetric chain carbonate and an asymmetric chain carbonate.   An electrochemical device comprising a positive electrode, a negative electrode and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, wherein the vinyl ester derivative represented by the general formula (I) is added to the non-aqueous electrolyte. A compound containing 0.1 to 5% by mass, further having S—O bond (A) and S═O bond (B) in the structure, and the total number of (A) and (B) being 3. The electrochemical element characterized by containing 0.1-5 mass%. The positive electrode is a positive electrode active material,
One or more selected from a lithium composite metal oxide containing at least one selected from cobalt, manganese, and nickel, and a lithium-containing olivine-type phosphate containing at least one selected from iron, cobalt, nickel, and manganese The electrochemical device according to claim 13, comprising: As the negative electrode active material, the negative electrode
14. The method according to claim 13, comprising at least one selected from lithium metal, a lithium alloy, a carbon material capable of occluding and releasing lithium, and a metal compound capable of occluding and releasing lithium including at least one of Sn and Si. The electrochemical element as described. From the X-ray diffraction measurement of the negative electrode sheet when the carbon material capable of inserting and extracting lithium is pressure-molded to a density of 1.5 g / cm ³ except for the current collector of the negative electrode. The ratio I (110) / I (004) of the peak intensity I (110) of the (110) plane and the peak intensity I (004) of the (004) plane of the obtained graphite crystal is 0.01 or more and 0.5 or less. The electrochemical device according to claim 15.