JP5376142B2 - Nonaqueous electrolyte and lithium battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte which has an excellent battery property such as a high temperature storage property in using the battery at a high voltage, and a cycle property, and a lithium battery using the same. <P>SOLUTION: There are provided a nonaqueous electrolyte including 0.001 to 5 mass% of an organic peroxide represented by a formula (I) based on an amount of the nonaqueous electrolyte in the nonaqueous electrolyte where an electrolyte salt is dissolved in a nonaqueous solvent, and a lithium battery using the same. In the formula, R<SP>1</SP>, R<SP>2</SP>, R<SP>3</SP>and R<SP>4</SP>represent a hydrogen atom, a straight or a branched 1-8C alkyl group, and the sum of the carbon number of R<SP>1</SP>and R<SP>2</SP>and the sum of the carbon number of R<SP>3</SP>and R<SP>4</SP>are 4 or larger, respectively. R<SP>1</SP>and R<SP>2</SP>, and R<SP>3</SP>and R<SP>4</SP>may form a ring mutually. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a non-aqueous electrolyte excellent in battery characteristics such as high-temperature storage characteristics and cycle characteristics when a battery is used at a high voltage, and a lithium battery using the same.

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as driving power sources for small electronic devices such as mobile phones and laptop computers, electric vehicles, and power storage sources.
The lithium secondary battery is mainly composed of a positive electrode and a negative electrode containing a material capable of inserting and extracting lithium, and a non-aqueous electrolyte containing a lithium salt. As the non-aqueous electrolyte, carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) are used.
As a negative electrode of a lithium secondary battery, lithium metal, a metal compound capable of inserting and extracting lithium (metal simple substance, oxide, alloy with lithium, etc.) and a carbon material are known. In particular, non-aqueous electrolyte secondary batteries using carbon materials that can occlude and release lithium such as coke and graphite (artificial graphite, natural graphite) are widely put into practical use.
Since the above negative electrode materials store and release lithium and electrons at a low potential equivalent to that of lithium metal, many solvents have the possibility of undergoing reductive decomposition, particularly at high temperatures. Regardless of this, the solvent in the electrolyte solution is partially reduced and decomposed on the negative electrode, and the decomposition product is deposited on the surface of the negative electrode to increase the resistance, or gas is generated due to the decomposition of the solvent and the battery is swollen. As a result, the movement of lithium ions is hindered, and there is a problem that battery characteristics such as cycle characteristics are deteriorated.

On the other hand, materials capable of inserting and extracting lithium such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiFePO ₄ used as positive electrode materials store and release lithium and electrons at a high voltage of 3.5 V or more based on lithium. Therefore, many solvents have the possibility of undergoing oxidative decomposition, and the solvent in the electrolyte solution partially oxidatively decomposes on the positive electrode regardless of the type of the positive electrode material, and the decomposition product is on the surface of the positive electrode. Lithium ion migration is hindered by increasing the resistance and increasing the resistance or by generating gas due to the decomposition of the solvent and causing the battery to swell, thereby degrading the battery characteristics such as cycle characteristics.

  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 high temperature is likely to deteriorate with a slight decomposition of the non-aqueous electrolyte.

In addition, as a lithium primary battery, for example, a lithium primary battery using manganese dioxide or graphite fluoride as a positive electrode and lithium metal as a negative electrode is known and widely used because of its high energy density, but it is stored for a long time. It is required to suppress an increase in internal resistance and improve long-term storage performance at high temperatures.
Furthermore, in recent years, as a new power source for electric vehicles or hybrid electric vehicles, from the viewpoint of output density, an electric double layer capacitor using activated carbon or the like as an electrode, a lithium ion secondary battery from the viewpoint of coexistence of energy density and output density Developed a power storage device called a hybrid capacitor (asymmetric capacitor that utilizes both the capacity of lithium storage and release and the electric double layer capacity), which combines the storage principle of an electric double layer capacitor and a cycle at high temperatures. Improvements in battery performance such as characteristics and high-temperature storage characteristics are demanded.

  Patent Document 1 discloses a lithium secondary battery using a nonaqueous electrolytic solution to which an organic peroxide such as cumene peroxide (dicumyl peroxide) or m-chloroperbenzoic acid is added. It has been shown that cycle characteristics can be improved when silicon or silicon-containing alloys are used.

International Publication WO2005 / 088761

  An object of the present invention is to provide a nonaqueous electrolytic solution excellent in battery characteristics such as high-temperature storage characteristics and cycle characteristics when the battery is used at a high voltage, and a lithium battery using the same.

  The present inventors have examined in detail the performance of the above-described prior art non-aqueous electrolyte. As a result, in the non-aqueous electrolyte of Patent Document 1, the cycle characteristics were never satisfactory, and there was no effect of suppressing an increase in resistance after high-temperature storage.

Accordingly, the inventors have conducted extensive research to solve the above-mentioned problems, and specified a specific amount of a six-membered organic peroxide having two peroxy structures (—O—O—) in the ring in the non-aqueous electrolyte. It has been found that a lithium battery excellent in battery characteristics such as high-temperature storage characteristics and cycle characteristics can be obtained by inclusion, and the present invention has been completed.
That is, the present invention provides the following (1) and (2).
(1) In a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, the organic peroxide represented by the following general formula (I) is contained in an amount of 0.001 to 5% by mass with respect to the non-aqueous electrolyte. A non-aqueous electrolyte characterized by:

(Wherein R ¹ , R ² , R ³ and R ⁴ each represent a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms, and the sum of R ¹ and R ² carbon atoms and R ³ and the sum of the carbon numbers of R ⁴ are each 4 or more, provided that R ¹ and R ² and R ³ and R ⁴ may each form a ring.
(2) In a lithium secondary battery comprising a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a non-aqueous solvent, the organic peroxide represented by the following general formula (I) is reduced with respect to the non-aqueous electrolyte solution. 0.001 to 5% by mass of a lithium battery.

(Wherein R ¹ , R ² , R ³ and R ⁴ are the same as described above.)

  According to the present invention, (1) a non-aqueous electrolyte excellent in battery characteristics such as high-temperature storage characteristics and cycle characteristics, and (2) a lithium battery using the non-aqueous electrolyte can be provided.

  Below, the nonaqueous electrolyte containing the organic peroxide of this invention and a lithium battery using the same are explained in full detail.

[Non-aqueous electrolyte]
The non-aqueous electrolyte of the present invention is a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, and a six-membered organic peroxide having two peroxy structures (—O—O—) in the ring. Is contained in an amount of 0.001 to 5% by mass with respect to the mass of the non-aqueous electrolyte.

[Organic peroxide]
The organic peroxide of the present invention is represented by the following general formula (I).

（式中、Ｒ^１、Ｒ^２、Ｒ^３及びＲ^４は、それぞれ水素原子または炭素数１〜８の直鎖もしくは分枝のアルキル基を表し、Ｒ^１及びＲ^２の炭素数の和並びにＲ^３及びＲ^４の炭素数の和がそれぞれ４以上である。但し、Ｒ^１及びＲ^２並びにＲ^３及びＲ^４はそれぞれ互いに環を形成してもよい。）

(Wherein R ¹ , R ² , R ³ and R ⁴ each represent a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms, and the sum of R ¹ and R ² carbon atoms and R ³ and the sum of the carbon numbers of R ⁴ are each 4 or more, provided that R ¹ and R ² and R ³ and R ⁴ may each form a ring.

The organic peroxide represented by the general formula (I) is not particularly limited, but specifically, 3,6-di-n-butyl-1,2,4,5-tetroxane (R ¹ = R ³ = hydrogen atom, R ² = R ⁴ = n-butyl group), 3,6-di-n-pentyl-1,2,4,5-tetroxane (R ¹ = R ³ = hydrogen atom, R ² = R ⁴ = n-pentyl group), 3,6-di-n-hexyl-1,2,4,5-tetroxane (R ¹ = R ³ = hydrogen atom, R ² = R ⁴ = n-hexyl group), 3 , 6-Di-n-heptyl-1,2,4,5-tetroxane (R ¹ = R ³ = hydrogen atom, R ² = R ⁴ = n-heptyl group), 3,6-di-n-octyl- 1,2,4,5-tetroxane (R ¹ = R ³ = hydrogen atom, R ² = R ⁴ = n-octyl group), 3,6-dimethyl-3,6-di -N-propyl-1,2,4,5-tetroxane (R ¹ = R ³ = methyl group, R ² = R ⁴ = n-propyl group), 3,6-dimethyl-3,6-di-n- Butyl-1,2,4,5-tetroxane (R ¹ = R ³ = methyl group, R ² = R ⁴ = n-butyl group), 3,6-dimethyl-3,6-di-n-pentyl-1 , 2,4,5-tetroxane (R ¹ = R ³ = methyl group, R ² = R ⁴ = n-pentyl group), 3,6-dimethyl-3,6-di (3-methyl-n-butyl) -1,2,4,5-tetroxane (R ¹ = R ³ = methyl group, R ² = R ⁴ = 3-methyl-n-butyl group), 3,6-dimethyl-3,6-di-n- Hexyl-1,2,4,5-tetroxane (R ¹ = R ³ = methyl group, R ² = R ⁴ = n-hexyl group), 3,6-diethyl-3 , 6-Di-n-butyl-1,2,4,5-tetroxane (R ¹ = R ³ = ethyl group, R ² = R ⁴ = n-butyl group), 3,6-diethyl-3,6- Di-n-pentyl-1,2,4,5-tetroxane (R ¹ = R ³ = ethyl group, R ² = R ⁴ = n-pentyl group), 3,6-diethyl-3,6-di (2 - methyl -n- butyl) -1,2,4,5-tetroxane ^(R 1 = R ³ = ^ethyl, R ^{2 =} R 4 ⁼ 2- methyl -n- butyl group), 3,3,6,6 - tetra -n- propyl-1,2,4,5-tetroxane ^{(R 1 = R 2 = R} 3 = R 4 = n- propyl group), 6,7,13,14- tetramethyl oxadiazole spiro [4. 2.4.2] tetradecane ^{(R 1} and ^{R 2} and ^{R 3} and ^{R 4} form a cyclopentane ring each other), 7,8, 5,16- tetra-oxa-di-spiro [5.2.5.2] hexadecane ^{(R 1} and ^{R 2} and ^{R 3} and ^{R 4} form a cyclohexane ring each other), 8,9,17,18- tetraoxa Dispiro [6.2.6.2] octodecane (R ¹ and R ² and R ³ and R ⁴ each form a cycloheptane ring with each other), 13, 14, 27, 28-tetraoxadispiro [11. 2.11.2] octacosane (R ¹ and R ² and R ³ and R ⁴ each form a cyclododecane ring each other), 6,7,14,15-tetraoxadispiro [4.2.5.2 ] pentadecane ^{(R 1} and ^{R 2} are a cyclopentane ring to form together, ^{R 3} and ^{R 4} form a mutually cyclohexane ring), 7,8,16,17- tetramethyl oxadiazole spiro [5 2.6.2] heptadecane ^{(R 1} and ^{R 2} together form a cyclohexane ring, ^{R 2} and ^{R 4} to each other form a cycloheptane ring), 6,7,14,15- tetramethyl oxadiazole spiro [4 2.5.2] pentadecane (R ¹ and R ² together form a cyclopentane ring and R ³ and R ⁴ together form a cyclohexane ring), 6,7,20,21-tetraoxadispiro [ 4.2.11.2] henicosan (R ¹ and R ² together form a cyclopentane ring and R ² and R ⁴ together form a cyclododecane ring), 7,8,21,22-tetraoxadi spiro [5.2.11.2] docosane ^{(R 1} and ^{R 2} are a cyclohexane ring to form together, ^{R 2} and ^{R 4} together form a cyclododecane ring) such as the high-temperature storage characteristics and cycle characteristics Preferable to further improve.
The sum of the carbon numbers of R ¹ and R ² and the sum of the carbon numbers of R ³ and R ⁴ may be the same or different, but both are 4 or more, and more preferably 5 or more. Moreover, as an upper limit of the sum total of the said carbon number, it is preferable that both are 12 or less, and it is still more preferable that it is 9 or less.
Among these, those in which R ¹ and R ² and R ³ and R ⁴ form a ring are particularly preferable, and 7,8,15,16-tetraoxadispiro [5.2.5.2] hexadecane (R ¹ And R ² and R ³ and R ⁴ each form a cyclohexane ring with each other).

[Content of organic peroxide]
In the nonaqueous electrolytic solution of the present invention, when the content of the organic peroxide represented by the general formula (I) contained in the nonaqueous electrolytic solution exceeds 5% by mass, an excessive film is formed on the electrode. As a result, battery characteristics such as high-temperature storage characteristics and cycle characteristics may be deteriorated, and if the amount is less than 0.001% by mass, a film is not sufficiently formed. The effect of improving the characteristics may not be obtained. Therefore, the content of the compound is 0.001% by mass or more with respect to the mass of the nonaqueous electrolytic solution, preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and 0.1% by mass. % Or more is more preferable. Moreover, the upper limit is 5 mass% or less, 3 mass% or less is more preferable, and 2 mass% or less is still more preferable.
It has been found that battery characteristics such as high temperature storage characteristics and cycle characteristics can be improved by adding the organic peroxide represented by the general formula (I). The reason is not necessarily clear, but is considered to be due to the following reason. The organic peroxide of the present invention contains two peroxy groups (—O—O—) in the cyclic structure as compared with dicumyl peroxide and m-chlorobenzoic acid having only one peroxy group. As a result, a highly oxidized film is formed on the positive electrode after decomposition, so that excessive oxidative decomposition of the non-aqueous electrolyte is suppressed, and a film with a high oxygen concentration is formed on the negative electrode. This is probably because ions easily move.

[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 and the like.
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, use of at least one selected from VC, VEC, FEC, and DFEC is preferable because battery characteristics such as high-temperature storage characteristics and cycle characteristics are further improved.
These solvents may be used alone, but when two or more kinds are used in combination, the effect of improving battery characteristics such as high-temperature storage characteristics and cycle characteristics is further improved, and preferably three or more kinds. Particularly preferred. Preferred combinations of these cyclic carbonates include EC and PC, FEC and PC, EC and VC, FEC and VC, PC and VC, EC and PC and VC, FEC and PC and VC, FEC and EC and PC and VC. Etc.
Although content in particular of cyclic carbonate is not restrict | limited, It is preferable to use in the range of 10-40 volume% with respect to the total volume of a nonaqueous solvent. When the content is less than 10% by volume, the electric conductivity of the electrolyte solution tends to be lowered and the cycle characteristics tend to be lowered. When the content exceeds 40% by volume, battery characteristics such as high-temperature storage characteristics and cycle characteristics tend to be lowered. There is. In particular, when 5 to 10% by volume of PC is contained, it is preferable because high temperature storage characteristics are improved.

Examples of chain carbonates include asymmetric chain carbonates such as methyl ethyl carbonate (MEC), methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, and ethyl propyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), and dipropyl. Examples include symmetric chain carbonates such as carbonate and dibutyl carbonate. In particular, inclusion of asymmetric chain carbonates is preferable because battery characteristics such as high-temperature storage characteristics and low-temperature cycle characteristics tend to be improved.
These chain carbonates may be used alone, but it is preferable to use a combination of two or more types because battery characteristics such as high-temperature storage characteristics and cycle characteristics are 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. When the content is less than 60% by volume, the viscosity of the electrolytic solution increases. When the content exceeds 90% by volume, the electrical conductivity of the electrolytic solution decreases, and battery characteristics such as high-temperature storage characteristics and cycle characteristics tend to decrease. Therefore, the above range is preferable.
The ratio of cyclic carbonates to chain carbonates is preferably 10:90 to 40:60 in terms of cyclic carbonates: chain carbonates (capacity ratio) from the viewpoint of improving battery characteristics such as high-temperature storage characteristics and cycle characteristics. 15:85 to 35:65 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 succinonitrile, glutaronite , Nitriles such as adiponitrile, 1,3-propane sultone, ethylene sulfite, 1,2-cyclohexanediol cyclic sulfite, 5-vinyl-hexahydro 1,3,2-benzodioxathiol-2-oxide, Examples thereof include S═O bond-containing compounds such as 1,4-butanediol dimethanesulfonate, 1,3-butanediol dimethanesulfonate, divinylsulfone, and bis (2-vinylsulfonylethyl) ether.

  Of the above non-aqueous solvents, ethers, nitriles, and S═O bond-containing compounds are preferably used in combination with the compound (I) because battery characteristics such as high-temperature storage characteristics and cycle characteristics are improved. When the addition amount of these compounds used in combination with compound (I) exceeds 5% by mass, the cycle characteristics may be deteriorated or the effect of improving the high-temperature storage characteristics may not be obtained. If it does not satisfy this condition, the effect of improving battery characteristics such as high-temperature storage characteristics and cycle characteristics may not be sufficiently obtained. Therefore, the content is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more with respect to the mass of the nonaqueous electrolytic solution. Moreover, the upper limit is preferably 5% by mass or less, and more preferably 3% by mass or less.

The above non-aqueous solvents are usually used as a mixture in order to achieve appropriate physical properties. The combination includes, for example, a combination of cyclic carbonates and chain carbonates, a combination of cyclic carbonates, chain carbonates and lactones, a combination of cyclic carbonates, chain carbonates and chain esters, cyclic Examples include combinations of carbonates, chain carbonates, and ethers, combinations of cyclic carbonates, chain carbonates, and nitriles, combinations of cyclic carbonates, chain carbonates, and S = O bond-containing compounds. .
Among these, it is preferable to use a non-aqueous solvent combining at least a cyclic carbonate and a chain carbonate in order to improve the effect of improving battery characteristics such as high-temperature storage characteristics and cycle characteristics. More specifically, a combination of one or more cyclic carbonates selected from EC, PC, VC, and FEC and one or more chain carbonates selected from DMC, MEC, and DEC can be given.

[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.

A preferable combination of these electrolyte salts includes a combination including LiPF ₆ and further including at least one selected from LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ C ₂ F ₅ ) _2. It is done. Preferably, a combination of LiPF ₆ and LiBF ₄ , a combination of LiPF ₆ and LiN (SO ₂ CF ₃ ) ₂ , a combination of LiPF ₆ and LiN (SO ₂ C ₂ F ₅ ) ₂ and the like can be mentioned. LiPF ₆ : [LiBF ₄ or LiN (SO ₂ CF ₃ ) ₂ or LiN (SO ₂ C ₂ F ₅ ) ₂ ] (molar ratio) when the ratio of LiPF ₆ is lower than 70:30, and from 99: 1 However, when the ratio of LiPF ₆ is high, the cycle characteristics may deteriorate. Therefore, LiPF ₆ : [LiBF ₄ or LiN (SO ₂ CF ₃ ) ₂ or LiN (SO ₂ C ₂ F ₅ ) ₂ ] (molar ratio) is preferably in the range of 70:30 to 99: 1, and 80:20 A range of ˜98: 2 is more preferred. By using in a combination of the above ranges, the effect of improving battery characteristics such as high-temperature storage characteristics and cycle characteristics can be further improved.
The electrolyte salt can be mixed in any proportion, but other electrolytes except LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ C ₂ F ₅ ) ₂ when used in combination with LiPF _6. If the ratio of the salt to the total electrolyte salt (molar fraction) is less than 0.01%, the effect of improving the high-temperature storage characteristics is poor, and if it exceeds 45%, the high-temperature storage characteristics may deteriorate. Therefore, the ratio (molar fraction) is preferably 0.01 to 45%, more preferably 0.03 to 20%, still more preferably 0.05 to 10%, and most preferably 0.05 to 5%. is there.
The concentration used by dissolving all the electrolyte salts is usually preferably 0.3M or more, more preferably 0.5M or more, and most preferably 0.7M or more with respect to the non-aqueous solvent. Moreover, the upper limit is preferably 2.5M or less, more preferably 2.0M or less, further preferably 1.5M or less, and most preferably 1.2M or less.

[Other additives]
By containing an aromatic compound in the nonaqueous electrolytic solution of the present invention, the safety of the battery during overcharge can be ensured. Preferable examples of such aromatic compounds include cyclohexylbenzene, fluorocyclohexylbenzene compounds (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), tert-butylbenzene. , Tert-amylbenzene, 1-fluoro-4-tert-butylbenzene, 1,3-di-tert-butylbenzene, biphenyl, terphenyl (o-, m-, p-isomer), diphenyl ether, fluorobenzene, difluoro Benzene (o-, m-, p-isomer), 2,4-difluoroanisole, partially hydrogenated terphenyl (1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexyl) Biff Yl) and the like.
These aromatic compounds are preferably added in an amount of 0.1 to 10% by mass relative to the mass of the non-aqueous electrolyte. These aromatic compounds may be used alone or in combination of two or more.

[Production of non-aqueous electrolyte]
The nonaqueous electrolytic solution of the present invention includes, for example, the organic nonoxidation represented by the general formula (I) with respect to the electrolyte salt and the mass of the nonaqueous electrolytic solution mixed with the nonaqueous solvent. It can be obtained by dissolving 0.001 to 5% by mass of the product.
At this time, it is preferable to use a nonaqueous solvent and a compound to be added to the electrolytic solution that are purified in advance and have as few impurities as possible within a range that does not significantly reduce productivity.
Battery characteristics such as long-term cycle characteristics and charge storage characteristics can be further improved by including, for example, air or carbon dioxide in the nonaqueous electrolytic solution of the present invention.
In the present invention, it is particularly preferable to use an electrolytic solution in which carbon dioxide is dissolved in a nonaqueous electrolytic solution from the viewpoint of improving charge / discharge characteristics at high temperatures. The dissolved amount of carbon dioxide is preferably 0.001% by mass or more, more preferably 0.05% by mass or more, more preferably 0.2% by mass or more, based on the mass of the non-aqueous electrolyte. Most preferably, the carbon dioxide is dissolved until saturation.
The nonaqueous electrolytic solution of the present invention can be suitably used as an electrolytic solution for a lithium primary battery and a lithium secondary battery. Furthermore, the nonaqueous electrolytic solution of the present invention can also be used as an electrolytic solution for electric double layer capacitors and an electrolytic solution for hybrid capacitors. Among these, the nonaqueous electrolytic solution of the present invention is most suitable for use in a lithium secondary battery.

〔Lithium battery〕
The lithium battery of the present invention is a generic term for a lithium primary battery and a lithium secondary battery, and comprises the non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a non-aqueous 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 the positive electrode active material for a lithium secondary battery, a composite metal oxide with lithium containing 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 oxides usable at 4.4 V or higher are more preferable. When a lithium transition metal composite oxide having a high charging voltage is used, battery characteristics such as high-temperature storage characteristics and cycle characteristics are likely to deteriorate due to a reaction with the electrolyte during charging. However, in the lithium secondary battery according to the present invention, A decrease in battery characteristics can be suppressed.

Furthermore, lithium-containing olivine-type phosphate can also be used as the positive electrode active material. 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 , VOx, 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 , Oxides of one or more metal elements such as Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , CoO, or sulfur compounds such as chalcogen compounds, SO ₂ , and SOCl ₂ And fluorocarbon (fluorinated graphite) represented by the general formula (CFx) n. Among 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 chemical changes. 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.

As the negative electrode active material for a lithium secondary battery, lithium metal, a lithium alloy, a carbon material capable of inserting and extracting lithium, a metal compound, and the like can be used singly or in combination of two or more.
Among these, it is 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 lattice spacing ( ₀₀₂ ) spacing (d ₀₀₂ ) is 0.340 nm ( It is particularly preferable to use a carbon material having a graphite-type crystal structure of nanometers) or less, particularly 0.335 to 0.337 nm. When a highly crystalline carbon material is used, it tends to react with the non-aqueous electrolyte during charging, and battery characteristics such as high-temperature storage characteristics and cycle characteristics tend to deteriorate. However, the lithium secondary battery according to the present invention has non-reactivity. Reaction with the water electrolyte can be suppressed. In addition, it is preferable that the highly crystalline carbon material is coated with the low crystalline carbon material because decomposition of the nonaqueous electrolytic solution is further suppressed.
Examples of the metal compound capable of inserting and extracting lithium as the negative electrode active material include Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, and Cu. , Zn, Ag, Mg, Sr, Ba, and other compounds containing at least one metal element. These metal compounds may be used in any form such as a simple substance, an alloy, an oxide, a nitride, a sulfide, a boride, and an alloy with lithium, but any of a simple substance, an alloy, an oxide, and an alloy with lithium. Is preferable because the capacity can be increased. Among these, those containing at least one element selected from Si, Ge and Sn are preferable, and those containing at least one element selected from Si and Sn are particularly preferable because the capacity of the battery can be increased.
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.
When graphite is used as the negative electrode active material, the density of the portion excluding the current collector of the negative electrode is usually 1.4 g / cm ³ or more, and preferably 1.6 g / cm ^{3 in} order to further increase the battery capacity. ³ or more, particularly preferably 1.7 g / cm ³ or more.

  Moreover, lithium metal or a lithium alloy is mentioned as a negative electrode active material for lithium primary batteries.

The structure of the lithium secondary battery is not particularly limited, and a coin battery, a cylindrical battery, a square battery, a laminate 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 of the present invention has excellent cycle characteristics over a long period of time even when the end-of-charge voltage is 4.2 V or higher, particularly 4.3 V or higher. Furthermore, even at 4.4 V, the cycle characteristics are It is good and the gas generation amount is also suppressed. 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 is used by 0.1-3C constant current discharge. Moreover, the lithium secondary battery in this invention can be charged / discharged at -40-100 degreeC, Preferably it is 0-80 degreeC.
In general, in a square battery, a laminated battery, and the like, the battery is structurally easy to swell due to the generation of gas, but the lithium secondary battery using the non-aqueous electrolyte of the present invention can suppress the swell due to gas generation.

  In the present invention, as a countermeasure against an increase in internal pressure of the lithium secondary battery, a method of providing a safety valve on the battery lid or incising 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.

Examples 1-10, Comparative Examples 1-3
[Production of lithium ion secondary battery]
LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ (positive electrode active material); 94% by mass, acetylene black (conductive agent); 3% by mass are mixed, and polyvinylidene fluoride (binder); 3% in advance. % Was added to the solution dissolved in 1-methyl-2-pyrrolidone and 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, and cut into a predetermined size to produce a belt-like positive electrode sheet. 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 (d ₀₀₂ = 0.335 nm, negative electrode active material) is added to a solution in which 5% by mass of polyvinylidene fluoride (binder) is previously dissolved in 1-methyl-2-pyrrolidone. And mixed to prepare a negative electrode mixture paste. This negative electrode mixture paste was applied to one side of a copper foil (current collector), dried and pressurized, and cut into a predetermined size to produce a strip-shaped negative electrode sheet. The density of the portion excluding the current collector of the negative electrode was 1.7 g / cm ³ . And it laminated | stacked in order of the positive electrode sheet | seat, the separator made from a microporous polyethylene film, and the negative electrode sheet | seat, and also added the organic peroxide of Table 1 similarly to the nonaqueous electrolyte of the composition of Table 1, and adjusted it. A non-aqueous electrolyte was added to prepare 2032 type coin batteries of Examples 1 to 10 and Comparative Examples 1 to 3, respectively.

[Evaluation of cycle characteristics]
Using the coin battery produced by the above method, in a constant temperature bath at 60 ° C., charge at a constant current of 1C and a constant voltage for 3 hours to a final voltage of 4.3V, and then to a final voltage of 3.0V under a constant current of 1C. Discharging was defined as one cycle, and this was repeated until 100 cycles were reached. And the discharge capacity maintenance factor after 100 cycles was calculated | required with the following formula | equation.
Discharge capacity retention ratio (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100
Table 1 shows battery fabrication conditions and battery characteristics.

[Evaluation of storage characteristics]
Using another coin battery using a non-aqueous electrolyte of the same composition as described above, charging was performed at a constant current of 1C and a constant voltage in a constant temperature bath at 25 ° C for 3 hours to a final voltage of 4.3V, and then a constant current of 1C. The battery was discharged to a lower end voltage of 3.0V. The average discharge voltage at the time of this discharge was taken as the average discharge voltage before storage. The battery was charged again with a constant current and a constant voltage of 1 C to a final voltage of 4.3 V for 3 hours, placed in a thermostat at 60 ° C., and stored at 4.3 V for 3 days. After that, put it in a constant temperature bath at 25 ° C., discharge once to a final voltage of 3.0 V under a constant current of 1 C, charge again to a final voltage of 4.3 V with a constant current and constant voltage of 1 C for 3 hours, and then to a constant voltage of 1 C. The battery was discharged to a final voltage of 3.0 V under the current. The average discharge voltage at the time of this discharge was taken as the average discharge voltage after storage. A coin battery was prepared and the battery characteristics were evaluated in the same manner as in Example except that 7,8,15,16-tetraoxadispiro [5.2.5.2] hexadecane was not added to the nonaqueous electrolyte. The average discharge voltage drop rate after storage was determined according to the following formula based on the comparative example 1.
Average discharge voltage drop rate (relative value) (%) = (average discharge voltage before storage−average discharge voltage after storage) / (average discharge voltage before storage in Comparative Example 1−average discharge after storage in Comparative Example 1) Voltage) x 100
Table 1 shows battery fabrication conditions and battery characteristics.

Example 11, Comparative Example 4
A positive electrode sheet was produced using LiFePO ₄ (positive electrode active material) instead of the positive electrode active material used in Example 3 and Comparative Example 1. LiFePO ₄ ; 90% by mass, acetylene black (conducting agent); 5% by mass were mixed, and a solution in which 5% by mass of polyvinylidene fluoride (binder) was previously dissolved in 1-methyl-2-pyrrolidone was mixed. In addition, the mixture was mixed to prepare a positive electrode mixture paste. This positive electrode mixture paste was applied onto an aluminum foil (current collector), dried, pressurized and cut into a predetermined size to produce a strip-like positive electrode sheet, cycle characteristics evaluation and storage characteristics. A coin battery was produced and evaluated in the same manner as in Example 3 and Comparative Example 1 except that the charge end voltage at the time of evaluation was 3.8 V and the discharge end voltage was 2.0 V. The results are shown in Table 2. The average discharge voltage drop rate after storage is a value calculated based on Comparative Example 4.

Example 12, Comparative Example 5
In Example 3 and Comparative Example 1, Si was used in place of artificial graphite as the negative electrode active material, 75% by mass of Si (negative electrode active material), 10% by mass of artificial graphite (conductive agent), acetylene black (conductive agent) 10% by mass and 5% by mass of polyvinylidene fluoride (binder) are mixed, and 1-methyl-2-pyrrolidone solvent is added to the mixture, and the mixture is applied onto a copper foil current collector and dried. In addition to the above, the non-aqueous electrolyte was prepared in the same manner as in Example 3 and Comparative Example 1 except that a strip-shaped negative electrode sheet was prepared by pressure treatment and cutting into a predetermined size, and a coin battery was prepared. Battery characteristics were measured. The results are shown in Table 3.

In any of the lithium secondary batteries of Examples 1 to 10, Comparative Example 1 in which the organic peroxide of the present invention is not added, dicumyl peroxide, m-chloroperbenzoic acid and the like have two peroxy structures ( Compared to the lithium secondary batteries of Comparative Example 2 and Comparative Example 3 to which a six-membered ring organic peroxide having —O—O—) was added, battery characteristics such as high-temperature storage characteristics and cycle characteristics were significantly improved. Yes.
Further, from the comparison between Example 11 and Comparative Example 4 and the comparison between Example 12 and Comparative Example 5, the same applies when lithium-containing olivine-type iron phosphate is used for the positive electrode or Si is used for the negative electrode. The effect is seen. 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 has an effect of improving the high temperature storage characteristics of the lithium primary battery.

  The lithium battery using the non-aqueous electrolyte of the present invention is excellent in battery characteristics such as high-temperature storage characteristics and cycle characteristics.

Claims (2)

In a non-aqueous electrolyte for a lithium battery in which an electrolyte salt is dissolved in a non-aqueous solvent, the organic peroxide represented by the following general formula (I) is contained in an amount of 0.001 to 5% by mass with respect to the non-aqueous electrolyte. A non-aqueous electrolyte for a lithium battery .

(Wherein R ¹ , R ² , R ³ and R ⁴ each represent a hydrogen atom or a linear or branched alkyl group having 1 to 8 carbon atoms, and the sum of R ¹ and R ² carbon atoms and R ³ and the sum of the carbon numbers of R ⁴ are each 4 or more, provided that R ¹ and R ² and R ³ and R ⁴ may each form a ring.
In a lithium battery comprising a non-aqueous electrolyte in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a non-aqueous solvent, an organic peroxide represented by the following general formula (I) Lithium battery characterized by containing -5 mass%.

(Wherein R ¹ , R ² , R ³ and R ⁴ are the same as described above.)