JP5391938B2 - Non-aqueous electrolyte and lithium secondary battery using the same - Google Patents

Non-aqueous electrolyte and lithium secondary battery using the same Download PDF

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JP5391938B2
JP5391938B2 JP2009203941A JP2009203941A JP5391938B2 JP 5391938 B2 JP5391938 B2 JP 5391938B2 JP 2009203941 A JP2009203941 A JP 2009203941A JP 2009203941 A JP2009203941 A JP 2009203941A JP 5391938 B2 JP5391938 B2 JP 5391938B2
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aqueous electrolyte
carbonate
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JP2011054490A (en
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正道 大貫
稔 古田土
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三菱化学株式会社
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage
    • Y02E60/12Battery technologies with an indirect contribution to GHG emissions mitigation
    • Y02E60/122Lithium-ion batteries

Description

  The present invention relates to a non-aqueous electrolyte and a lithium secondary battery using the same.

Lithium secondary batteries have the advantages of high energy density and less self-discharge. Therefore, in recent years, it has been widely used as a power source for consumer mobile devices such as mobile phones, notebook computers, and PDAs.
An electrolytic solution for a normal lithium secondary battery has a lithium salt as a supporting electrolyte and a non-aqueous organic solvent as main components. The non-aqueous organic solvent used is required to have a high dielectric constant in order to dissociate the lithium salt, to exhibit high ionic conductivity in a wide temperature range, and to be stable in the battery. Since it is difficult to achieve these requirements with a single solvent, usually a combination of a high boiling point solvent typified by propylene carbonate, ethylene carbonate and the like and a low boiling point solvent such as dimethyl carbonate, diethyl carbonate, Used as a non-aqueous solvent.

In addition, lithium secondary batteries require various characteristics such as initial capacity, rate characteristics, cycle characteristics, high temperature storage characteristics, low temperature characteristics, continuous charge characteristics, self-discharge characteristics, and overcharge prevention characteristics. Many methods have been reported so far for improving the amount of various auxiliary agents contained in the electrolyte for improvement. For example, it has been proposed to contain an acid anhydride as an auxiliary agent.
Patent Document 1 discloses that the storage characteristics in a temperature atmosphere exceeding 100 ° C. can be improved by using an electrolytic solution in which 0.3 to 3% of an acid anhydride and a cyclic sultone derivative are added. . Patent Document 2 discloses that cycle characteristics and high-temperature storage characteristics are improved by using a negative electrode containing CoSnC or the like as an active material and using an electrolytic solution containing acid anhydride and fluoroethylene carbonate. Yes. Patent Document 3 discloses that the discharge capacity maintenance rate is improved in cycle characteristics by using a silicon alloy negative electrode and using an electrolytic solution containing an acid anhydride and a halogen atom-containing carbonate.

  Patent Document 4 discloses that in a battery having an open circuit voltage of 4.25 V to 6.00 V, cycle characteristics are improved by using an electrolytic solution containing acid anhydrides and a cyclic carbonate having a halogen atom. Is disclosed. Patent Document 5 discloses an electrolytic solution containing an acid anhydride and halogen-substituted ethylene carbonate.

JP 2004-47413 A JP 2006-156331 A JP 2007-299541 A JP 2008-198432 A US Patent Publication No. 2007/0042267

  In recent years, the demand for higher performance of lithium secondary batteries has been increasing, and various characteristics such as high capacity, cycle characteristics, high-temperature storage characteristics, continuous charge characteristics, and overcharge characteristics can be achieved together at a high level. It is demanded. Many methods for improving cycle characteristics and high-temperature storage characteristics have been proposed, but there are few reports on methods for improving continuous charge characteristics. When the present inventors examined, the technique currently disclosed by patent documents 1-5 was inadequate for improving a continuous charge characteristic.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a lithium secondary battery having improved characteristics such as cycle characteristics and storage characteristics, in particular, continuous charge characteristics.

As a result of intensive studies to solve the above problems, the inventors of the present invention contain a cyclic carbonate having a fluorine substituent and / or a carbon-carbon unsaturated bond, and further a cyclic acid anhydride and an S═O group. It has been found that by using a non-aqueous electrolyte solution containing a specific amount of the organic compound contained relative to the weight of the non-aqueous electrolyte, various characteristics such as cycle characteristics and storage characteristics, in particular, continuous charging characteristics are improved. Was completed.
That is, the gist of the present invention is as shown in the following (1) to (7).

(1) In a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous organic solvent, the non-aqueous organic solvent contains a cyclic carbonate having a fluorine substituent and / or a carbon-carbon unsaturated bond, and the non-aqueous electrolyte The non-aqueous electrolytic solution, wherein the electrolytic solution contains a cyclic acid anhydride and an S = O group-containing organic compound in an amount of 0.001 to 0.5 % by weight and 0.001 to 10% by weight, respectively, based on the weight of the non-aqueous electrolyte. .

(2) The non-aqueous electrolyte according to (1) above, wherein the cyclic acid anhydride is a cyclic acid anhydride having a carbon-carbon unsaturated bond.
(3) The nonaqueous electrolytic solution according to (1) or (2) above, wherein the cyclic acid anhydride is a cyclic acid anhydride having a molecular weight of 250 or less.
(4) The organic compound containing S═O group is at least one selected from the group consisting of sulfoxides, sulfites, sulfones, sulfonates, sultones and sulfates. The non-aqueous electrolyte solution according to any one of 3).

(5) The cyclic acid anhydride and the S = O group-containing organic compound are contained in an amount of 0.001 to 0.25% by weight and 0.001 to 5% by weight, respectively, based on the weight of the nonaqueous electrolytic solution. (4) The nonaqueous electrolytic solution according to any one of (4).
(6) The non-aqueous electrolyte solution according to any one of (1) to (5) above, wherein the fluorine-substituted cyclic carbonate is a carbonate represented by the general formula (1).

(Wherein, in each of R 1 to R 4 independently represents a hydrogen atom, a fluorine atom, an alkyl group or a fluorine-substituted alkyl group having 1 to 4 carbon atoms, 1 to 4 carbon atoms, the R 1 to R 4 At least one is a fluorine atom or a C1-C4 fluorine-substituted alkyl group.)

(7) The above-mentioned (1) to (6), wherein the cyclic carbonate having a carbon-carbon unsaturated bond is at least one selected from the group consisting of vinylene carbonate derivatives and vinylethylene carbonate derivatives. The nonaqueous electrolytic solution according to any one of the above.
(8) A non-aqueous electrolyte battery including a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution is any one of (1) to (7) above A lithium secondary battery, which is a non-aqueous electrolyte.

  According to the present invention, when used in a lithium secondary battery, various characteristics such as cycle characteristics and storage characteristics, in particular, a non-aqueous electrolyte solution capable of greatly improving continuous charge characteristics, and the above-mentioned using the electrolyte solution A lithium secondary battery with improved characteristics can be provided.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments, and can be arbitrarily modified without departing from the gist of the present invention.
The non-aqueous electrolyte solution of the present invention contains a lithium salt and a non-aqueous organic solvent as main components. In addition, the lithium secondary battery of the present invention includes a non-aqueous electrolyte, and a positive electrode and a negative electrode that can occlude and release lithium ions. In addition, the lithium secondary battery of the present invention may include other components.

[I. Non-aqueous electrolyte]
The non-aqueous electrolyte solution of the present invention (hereinafter appropriately referred to as “non-aqueous electrolyte solution in the present invention”) is a non-aqueous electrolyte obtained by dissolving a lithium salt in a non-aqueous organic solvent (hereinafter appropriately referred to as “non-aqueous organic solvent in the present invention”) In the aqueous electrolyte, the non-aqueous organic solvent contains a cyclic carbonate having a fluorine substituent and / or a carbon-carbon unsaturated bond, and the non-aqueous electrolyte further contains a cyclic acid anhydride (hereinafter referred to as “the present invention”). And an S = O group-containing organic compound (hereinafter referred to as “the S═O group-containing organic compound in the present invention” as appropriate) in an amount of 0.001 to 1 weight relative to the weight of the non-aqueous electrolyte. % And 0.001 to 10% by weight of non-aqueous electrolyte.

[1. Cyclic carbonate having a fluorine substituent]
[1-1. type]
The cyclic carbonate having a fluorine substituent in the present invention is not particularly limited as long as it is a cyclic carbonate in which any hydrogen atom in the molecule of the cyclic carbonate such as ethylene carbonate or propylene carbonate is substituted with fluorine, but the following general formula What is represented by (1) is preferable.

(Wherein R 1 to R 4 are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorine-substituted alkyl group having 1 to 4 carbon atoms, and at least one of R 1 to R 4 One is a fluorine atom or a fluorine-substituted alkyl group having 1 to 4 carbon atoms.)

In the general formula (1), R 1 to R 4 are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 4 carbon atoms, or a fluorine-substituted alkyl group having 1 to 4 carbon atoms, and R 1 to R 4 At least one of 4 is a fluorine atom or a fluorine-substituted alkyl group having 1 to 4 carbon atoms.
Preferred alkyl groups include a methyl group, an ethyl group, a propyl group, and a butyl group. Among them, a methyl group and an ethyl group are more preferable, and a methyl group is most preferable. Examples of the fluorine-substituted alkyl group having 1 to 4 carbon atoms include a monofluoromethyl group, a difluoromethyl group, a trimethylfluoromethyl group, a 2,2,2-trifluoroethyl group, and a pentafluoroethyl group. However, a trifluoromethyl group and a 2,2,2-trifluoroethyl group are more preferable.

Specific examples of the cyclic carbonate having a fluorine substituent in the present invention include fluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro. -1-methylethylene carbonate, 1,2-difluoro-1,2-dimethylethylene carbonate, tetrafluoroethylene carbonate, monofluoromethyl ethylene carbonate, difluoromethyl ethylene carbonate, trifluoromethyl ethylene carbonate, 2,2,2-tri Examples thereof include fluoroethyl ethylene carbonate. Among these, fluoroethylene carbonate, 1,2-difluoroethylene carbonate, and trifluoromethylethylene carbonate are more preferable.
Moreover, the cyclic carbonate which has a fluorine substituent in this invention mentioned above may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

[1-2. composition]
The content of the cyclic carbonate having a fluorine substituent in the present invention is usually 0.01% by volume or more, preferably 0.1% by volume or more, more preferably 1% by volume with respect to the total volume of the non-aqueous organic solvent. Above, more preferably 5% by volume or more, and usually 50% by volume or less, preferably 30% by volume or less, more preferably 20% by volume or less. If the content is too large, the high-temperature storage characteristics tend to deteriorate, and furthermore, the cost becomes high because the fluorine-substituted cyclic carbonate is expensive. Moreover, when content is too small, the effect of this invention may not fully be exhibited.

[2. Cyclic carbonate having a carbon-carbon unsaturated bond]
[2-1. type]
The cyclic carbonate having a carbon-carbon unsaturated bond in the present invention is not particularly limited as long as it is a cyclic carbonate having a carbon-carbon double bond and / or a carbon-carbon triple bond in the molecule, and an arbitrary one is used. Can do. A cyclic carbonate having a carbon-carbon double bond is preferred from the viewpoint of being chemically and electrochemically more stable.

  Specifically, vinylene carbonate derivatives such as vinylene carbonate, methyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate; vinyl ethylene carbonate, 1,1-divinyl ethylene carbonate, Examples thereof include vinylethylene carbonate derivatives such as 1,2-divinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, and 1-phenyl-2-vinylethylene carbonate. Among these, vinylene carbonate derivatives such as vinylene carbonate, methyl vinylene carbonate and 1,2-dimethyl vinylene carbonate; vinyl ethylene carbonate derivatives such as vinyl ethylene carbonate and 1,2-divinyl ethylene carbonate are preferable. In particular, vinylene carbonate and vinyl ethylene carbonate are more preferable.

  The cyclic carbonate having a carbon-carbon unsaturated bond in the present invention may further have a fluorine substituent in the molecule. Also in this case, the carbon-carbon unsaturated bond is preferably a double bond. Examples of the cyclic carbonate having a carbon-carbon unsaturated bond and fluorine substitution include fluorovinylene carbonate, 1,2-difluorovinylene carbonate, 1-fluoro-2-methylvinylene carbonate, 1-fluoro-2-phenylvinylene carbonate, etc. Vinylene carbonate derivatives such as 1-fluoro-2-vinylethylene carbonate.

In addition, the cyclic carbonate which has a carbon-carbon unsaturated bond may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.
The carbon number of the cyclic carbonate having a carbon-carbon unsaturated bond is usually 3 or more, and usually 20 or less, preferably 15 or less. Furthermore, the molecular weight of the cyclic carbonate having a carbon-carbon unsaturated bond is usually 80 or more, and usually 250 or less, preferably 150 or less. If the carbon number or molecular weight is too large, the solubility in the electrolytic solution is deteriorated, and the effects of the present invention may not be sufficiently exhibited.

[2-2. composition]
The content of the cyclic carbonate having a carbon-carbon unsaturated bond in the present invention is usually 0.01% by volume or more, preferably 0.1% by volume or more, more preferably based on the total volume of the non-aqueous organic solvent. 1 volume% or more, usually 20 volume% or less, preferably 10 volume% or less, more preferably 5 volume% or less. When there is too much content, there exists a tendency for a high temperature storage characteristic to deteriorate. Moreover, when content is too small, the effect of this invention may not fully be exhibited.

[3. Cyclic acid anhydride]
[3-1. type]
The cyclic acid anhydride in the present invention is not particularly limited as long as it is a cyclic acid anhydride. Examples of these are succinic anhydride, methyl succinic anhydride, 2,2-dimethyl succinic anhydride, 2,3-dimethyl succinic anhydride, 2,2,3-trimethyl succinic anhydride, 2,2, 3,3-tetramethyl succinic anhydride, vinyl succinic anhydride, 2,3-divinyl succinic anhydride, phenyl succinic anhydride, 2,3-diphenyl succinic anhydride, maleic anhydride, citraconic anhydride, Itaconic anhydride, phthalic anhydride, pyromellitic anhydride, glutaric anhydride, glutaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 5-norbornene- 2,3-dicarboxylic anhydride, 2-phenylglutaric anhydride, 2-sulfobenzoic anhydride, hexafluoroglutaric anhydride, etc. It is below.

  The cyclic acid anhydride in the present invention is preferably a cyclic acid anhydride having a carbon-carbon unsaturated bond. This is because the reduction potential is more noble, so that it is reduced during the initial charge and a protective film is more easily formed on the negative electrode. Examples include maleic anhydride, phthalic anhydride, pyromellitic anhydride, itaconic anhydride, citraconic anhydride, phenylsuccinic anhydride, 2-phenylglutaric anhydride, 2-sulfobenzoic anhydride, cyclopentene dicarboxylic acid. Anhydrides, cyclohexene dicarboxylic acid anhydrides, monofluoromaleic acid anhydrides, 2,3-difluoromaleic acid anhydrides, trifluoromethylmaleic acid anhydrides and the like can be mentioned. Of these, itaconic anhydride, citraconic anhydride, phenylsuccinic anhydride, phthalic anhydride, cyclopentene dicarboxylic acid anhydride, cyclohexene dicarboxylic acid anhydride, and trifluoromethylmaleic acid anhydride are particularly preferable.

The molecular weight of these acid anhydrides is usually 300 or less, more preferably 250 or less, and still more preferably 180 or less. If the molecular weight is too large, it may not dissolve in the non-aqueous organic solvent.
Moreover, the cyclic acid anhydride in this invention mentioned above may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

[3-2. composition]
The content of the cyclic acid anhydride in the present invention is 0.001% by weight or more, preferably 0.01% by weight or more, more preferably 0.03% by weight or more, based on the total weight of the non-aqueous electrolyte. More preferably 0.05% by weight or more, 1.5% by weight or less, preferably 1.0% by weight or less, more preferably 0.5% by weight or less, still more preferably 0.25% by weight or less, most preferably 0.2% by weight or less. When the content is too large, the negative electrode resistance tends to increase and the capacity tends to decrease. Moreover, when content is too small, the effect of this invention may not fully be exhibited.

[4. S = O group-containing organic compound]
[4-1. type]
The S = O group-containing organic compound in the present invention is not particularly limited as long as it is an organic compound containing an S = O group in the molecule. Examples of these include sulfoxides, sulfites, sulfones, sulfonates, sultones, and sulfates, with sulfites, sulfones, sulfonates, and sultones being preferred.

Examples of sulfites include dimethyl sulfite, diethyl sulfite, ethylene sulfite, and propylene sulfite. Among these, dimethyl sulfite and ethylene sulfite are preferable.
Examples of sulfones include symmetrical chain sulfones such as dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone, and divinyl sulfone; methyl ethyl sulfone, methylpropyl sulfone, methyl phenyl sulfone, methyl vinyl sulfone, ethyl phenyl sulfone, ethyl Examples include asymmetric chain sulfones such as vinyl sulfone and phenyl vinyl sulfone; and cyclic sulfones such as sulfolane and sulfolene. Among these, methylsulfones such as dimethylsulfone, methylethylsulfone, methylpropylsulfone, methylvinylsulfone, and divinylsulfone are preferable.

  Examples of sulfonates are methyl methane sulfonate, ethyl methane sulfonate, phenyl methane sulfonate, methyl ethane sulfonate, ethyl ethane sulfonate, phenyl ethane sulfonate, methyl benzene sulfonate, ethyl benzene sulfonate, phenyl benzene sulfonate, busulfan, 1,4-butanediol bis. (2,2,2-trifluoromethanesulfonate), 1,4-butanediol bis (2,2,2-trifluoroethanesulfonate), 1,2,4-butanetrioltrimethanesulfonate and the like. Among these, methanesulfonates such as methylmethanesulfonate, ethylmethanesulfonate, and phenylmethanesulfonate, and busulfan, 1,4-butanediol bis (2,2,2-trifluoromethanesulfonate), 1,4-butanediol bis (2 , 2,2-trifluoroethanesulfonate).

Examples of sultone include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, 1,4-butene sultone and the like. Among these, 1,3-propane sultone and 1,3-propene sultone are preferable.
Moreover, the S = O group containing organic compound in this invention mentioned above may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

[4-2. composition]
In the present invention, the content of the S═O group-containing organic compound is 0.001% by weight or more, preferably 0.01% by weight or more, more preferably 0.1% by weight with respect to the total weight of the non-aqueous electrolyte. % Or more, more preferably 0.3% by weight or more, and 10% by weight or less, preferably 5% by weight or less, more preferably 3% by weight or less, and further preferably 2% by weight or less. When the content is too large, the negative electrode resistance tends to increase and the capacity tends to decrease. Moreover, when content is too small, the effect of this invention may not fully be exhibited.

[5. Nonaqueous organic solvent other than cyclic carbonate having fluorine substituent and / or carbon-carbon unsaturated bond]
[5-1. type]
The non-aqueous organic solvent in the present invention contains a cyclic carbonate having a fluorine substituent and / or a carbon-carbon unsaturated bond as described above, but there is no particular limitation on the other solvent, and a known organic solvent is used. It is possible. Examples of these are cyclic carbonates that are not fluorine-substituted and have no carbon-carbon unsaturated bond, chain carbonates, chain esters, cyclic esters (lactone compounds), chain ethers, cyclic Examples include ethers, nitrogen-containing organic solvents, and sulfur-containing organic solvents. Of these, cyclic carbonates, chain carbonates, chain esters, cyclic esters, chain ethers, cyclic ethers, and nitrogen-containing organic solvents are usually preferred as solvents that exhibit high ionic conductivity.

  Examples of cyclic carbonates that are not fluorine-substituted and have no carbon-carbon unsaturated bond include ethylene carbonate, propylene carbonate, butylene carbonate, dimethylethylene carbonate, diethylethylene carbonate, monopropylethylene carbonate, and dipropylethylene. Examples include carbonate, phenylethylene carbonate, diphenylethylene carbonate, catechol carbonate, and the like. Among these, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, and butylene carbonate is preferable. Furthermore, ethylene carbonate and / or propylene carbonate are particularly preferable.

  Examples of the chain carbonates include carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propyl methyl carbonate, dipropyl carbonate, methyl phenyl carbonate, ethyl phenyl carbonate, diphenyl carbonate; bis (trifluoromethyl) carbonate, Examples include halogen-substituted carbonates such as methyl trifluoromethyl carbonate, bis (monofluoroethyl) carbonate, methyl monofluoroethyl carbonate, bis (trifluoroethyl) carbonate, and methyl trifluoroethyl carbonate. Among these, it is preferably at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate and ethyl propyl carbonate, and more preferably a group consisting of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate. Particularly preferred is at least one selected from the group consisting of

Specific examples of the chain esters include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate. Among these, ethyl acetate, methyl propionate, and methyl butyrate are preferable.
Specific examples of cyclic esters include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, δ-valerolactone, and the like. Among these, γ-butyrolactone is preferable.

Specific examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether and the like.
Specific examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane and the like.
Further, specific examples of the nitrogen organic solvent include N-methylpyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, and acetonitrile.

[5-2. Composition ratio]
In the non-aqueous organic solvent in the present invention, as a solvent other than cyclic carbonates that are not fluorine-substituted and do not have a carbon-carbon unsaturated bond, one kind may be used alone, or two or more kinds may be arbitrarily selected. However, it is preferable to use a mixture of two or more solvents.

  In particular, it is preferable to mainly consist of cyclic carbonates that are not fluorine-substituted and have no carbon-carbon unsaturated bonds, and chain carbonates or chain esters. Here, mainly, specifically, the non-aqueous organic solvent is a cyclic carbonate that is not fluorine-substituted and has no carbon-carbon unsaturated bond, and a chain carbonate or a chain ester. Of 50% by volume or more in total. Furthermore, the ratio of the cyclic carbonates not substituted with fluorine and having no carbon-carbon unsaturated bond is usually 5% by volume or more, preferably 10% by volume or more, more preferably 15% by volume or more, Usually, it is 50 volume% or less, preferably 40 volume% or less, more preferably 30 volume% or less.

  If the lower limit of the above range is not reached, the lithium salt is less likely to dissociate and the conductivity is reduced, so the high load capacity tends to decrease.If the upper limit is exceeded, the viscosity becomes too high and Li ions are difficult to move, resulting in a high load. The capacity tends to decrease.

[6. Lithium salt]
Lithium salt is used as an electrolyte. There is no restriction | limiting in particular in the kind of lithium salt, You may use any of inorganic lithium salt and organic lithium salt.
Examples of inorganic lithium salts include inorganic fluoride salts such as LiPF 6 , LiAsF 6 , LiBF 4 and LiSbF 6 ; inorganic chloride salts such as LiAlCl 4 ; perhalogenates such as LiClO 4 , LiBrO 4 and LiIO 4. Etc.
Examples of organic lithium salts include perfluoroalkane sulfonates such as CF 3 SO 3 Li and C 4 F 9 SO 3 Li; perfluoroalkane carboxylates such as CF 3 COOLi; (CF 3 CO) Perfluoroalkanecarbonimide salts such as 2 NLi; fluorine-containing organic lithium salts such as perfluoroalkanesulfonimide salts such as (CF 3 SO 2 ) 2 NLi and (C 2 F 5 SO 2 ) 2 NLi.

Among these, LiPF 6 , LiBF 4 , CF 3 SO 3 Li, (CF 3 SO 2 ) 2 NLi, and the like are preferable because they are easily soluble in non-aqueous organic solvents and exhibit a high degree of dissociation.
In addition, lithium salt may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.
In particular, the combined use of LiPF 6 and LiBF 4 or the combined use of LiPF 6 and (CF 3 SO 2 ) 2 NLi is preferable because it has an effect of improving the continuous charge characteristics.

  Furthermore, the concentration of the lithium salt in the non-aqueous electrolyte solution is arbitrary as long as the effects of the present invention are not significantly impaired, but usually 0.5 mol / L or more, preferably 0.75 mol / L with respect to the non-aqueous electrolyte solution. L or more, and usually 2 mol / L or less, preferably 1.75 mol / L or less. If the concentration of the lithium salt is too low, the electric conductivity of the non-aqueous electrolyte may be insufficient. On the other hand, if the concentration of the lithium salt is too high, the electrical conductivity is lowered due to an increase in viscosity, and precipitation at a low temperature is likely to occur, and the performance of the lithium secondary battery tends to be lowered.

[7. Film-forming agent]
The nonaqueous electrolytic solution according to the present invention preferably further contains one kind of monofluorophosphate and difluorophosphate for the purpose of forming a film on the negative electrode and improving battery characteristics. Monofluorophosphate and difluorophosphate are preferably sodium monofluorophosphate, lithium monofluorophosphate, potassium monofluorophosphate, sodium difluorophosphate, lithium difluorophosphate, and potassium difluorophosphate. Particularly preferred are lithium monofluorophosphate and lithium difluorophosphate.

  The concentration of monofluorophosphate and difluorophosphate is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 0.2% by weight or more, and usually 10% by weight based on the entire electrolyte. % By weight or less, preferably 3% by weight or less, more preferably 2% by weight or less, and further preferably 1% by weight or less. If the concentrations of monofluorophosphate and difluorophosphate are too high, the reaction resistance of the negative electrode tends to increase and the capacity tends to decrease. On the other hand, if the concentration is too small, the effects of the present invention may not be sufficiently exhibited.

[8. Other auxiliaries]
The non-aqueous electrolyte in the present invention may contain other auxiliary agents for the purpose of improving the wettability, overcharge characteristics, etc. of the non-aqueous electrolyte in a range that does not significantly impair the effects of the present invention.
Examples of auxiliaries include carboxylic acid esters such as vinyl acetate, divinyl adipate, and allyl acetate; t-butylbenzene, t-amylbenzene, biphenyl, o-terphenyl, 2-fluorobiphenyl, 4-fluorobiphenyl, 2 Aromatic compounds such as 1,4-difluorobiphenyl, fluorobenzene, 2,4-difluorobenzene, cyclohexylbenzene, diphenyl ether, 2,4-difluoroanisole, 3,5-difluoroanisole, trifluoromethylbenzene and the like And those substituted with a fluorine atom. Moreover, 1 type may be used independently for an adjuvant, and 2 or more types may be used together by arbitrary combinations and a ratio.

  Further, the concentration of the auxiliary agent in the non-aqueous electrolyte solution is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.01% by weight or more, preferably 0.1% by weight or more, and usually 5% by weight. % Or less, preferably 3% by weight or less. In addition, when using 2 or more types of adjuvants together, it is preferable that the sum of these concentrations falls within the above range.

[9. Non-aqueous electrolyte state]
When used in the lithium secondary battery of the present invention, the nonaqueous electrolytic solution is usually present in a liquid state. For example, the nonaqueous electrolytic solution may be gelled with a polymer to form a semi-solid electrolyte. The polymer used for the gelation is arbitrary, and examples thereof include polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyethylene oxide, polyacrylate, and polymethacrylate. In addition, the polymer | macromolecule used for gelatinization may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  Moreover, when using a non-aqueous electrolyte as a semi-solid electrolyte, the ratio of the non-aqueous electrolyte in the semi-solid electrolyte is arbitrary as long as the effects of the present invention are not significantly impaired. As a suitable range, the ratio of the non-aqueous electrolyte to the total amount of the semisolid electrolyte is usually 30% by weight or more, preferably 50% by weight or more, more preferably 75% by weight or more, and usually 99.95. % By weight or less, preferably 99% by weight or less, more preferably 98% by weight or less. If the ratio of the non-aqueous electrolyte is too large, it may be difficult to hold the electrolyte and the liquid may easily leak. Conversely, if it is too small, the charge / discharge efficiency and the capacity may be insufficient.

[10. Method for producing non-aqueous electrolyte]
The method for producing the non-aqueous electrolyte in the present invention is not particularly limited. For example, a lithium salt is added to a non-aqueous organic solvent containing a cyclic carbonate containing a fluorine substituent and / or a carbon-carbon unsaturated bond. The cyclic acid anhydride and S = O group-containing organic compound in the present invention can be prepared by adding 0.001 to 1.5% by weight and 0.001 to 10% by weight, respectively, with respect to the weight of the non-aqueous electrolyte. .

  In preparing the non-aqueous electrolyte, each raw material of the non-aqueous electrolyte, that is, a lithium salt, a cyclic carbonate having a fluorine substituent and / or a carbon-carbon unsaturated bond in the present invention, other non-aqueous organic solvents, The cyclic acid anhydride, the S = O group-containing organic compound and other auxiliary agents in the present invention are preferably dehydrated in advance. If water is present in the non-aqueous electrolyte, electrolysis of water, reaction between water and lithium metal, hydrolysis of lithium salt, and the like may occur, which is not preferable. As the degree of dehydration, it is desirable to dehydrate until the water content is usually 50 ppm or less, preferably 30 ppm or less. In the present specification, ppm means a ratio based on weight.

The dehydration means is not particularly limited. For example, when the object to be dehydrated is a liquid such as a non-aqueous organic solvent, a molecular sieve or the like may be used. When the object to be dehydrated is a solid such as an electrolyte, it may be dried at a temperature lower than the temperature at which decomposition occurs.
[11. mechanism]
The mechanism by which the effect of the present invention can be obtained is not clear, but is considered as follows.

  In the present invention, a part of the cyclic acid anhydride is reduced during the initial charging of battery production, and a protective film is formed on the negative electrode. However, since this protective film gradually dissolves in a solvent containing a cyclic carbonate containing a fluorine-substituted and / or carbon-carbon unsaturated bond, it has a problem that the negative electrode cannot be protected continuously. In a negative electrode that is not protected by a coating, reductive decomposition of a solvent or the like proceeds to increase resistance, and lithium is deposited during charging, leading to a decrease in capacity.

On the other hand, since the protective film formed from a cyclic acid anhydride is difficult to dissolve in a solvent not containing a cyclic carbonate containing a fluorine-substituted and / or carbon-carbon unsaturated bond, no adverse effect is observed. That is, the above-mentioned problems are limited to the case where a solvent containing a cyclic carbonate containing a fluorine substitution and / or a carbon-carbon unsaturated bond is used.
This problem can be solved by allowing a specific amount of the S═O group-containing organic compound in the present invention to be present in the electrolytic solution. When the cyclic acid anhydride in the present invention is reduced during initial charging, a part of the S═O group-containing organic compound reacts and is taken into the negative electrode film. That is, the presence of the S═O group-containing organic compound forms a hybrid film derived from the cyclic acid anhydride and the S═O group-containing organic compound on the negative electrode. Since this hybrid film is difficult to dissolve in a solvent containing a fluorine-substituted cyclic carbonate, the reaction on the negative electrode is suppressed and lithium is difficult to deposit during charging. Therefore, capacity deterioration when continuous charging is performed is reduced.

[II. Lithium secondary battery]
The lithium secondary battery of the present invention comprises the above-described non-aqueous electrolyte of the present invention, and a positive electrode and a negative electrode capable of inserting and extracting lithium ions. In addition, the lithium secondary battery of the present invention may have other configurations. For example, a lithium secondary battery usually includes a spacer.

[1. Positive electrode]
As long as the positive electrode can occlude and release lithium, any positive electrode can be used as long as the effects of the present invention are not significantly impaired.
Usually, a positive electrode having a positive electrode active material layer provided on a current collector is used. Note that the positive electrode may include other layers as appropriate.

[1-1. Positive electrode active material layer]
The positive electrode active material layer includes a positive electrode active material. The positive electrode active material is not limited as long as it can occlude and release lithium ions. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides of transition metals and lithium, and sulfides of transition metals.

Specific examples of transition metal oxides include MnO, V 2 O 5 , V 6 O 13 , and TiO 2 . Specific examples of the composite oxide of transition metal and lithium include a lithium nickel composite oxide whose basic composition is LiNiO 2 ; a lithium cobalt composite oxide whose basic composition is LiCoO 2 ; a basic composition of LiMnO 2 and LiMnO. And lithium manganese composite oxide such as 4 . Further, specific examples of the transition metal sulfide include TiS 2 and FeS.

Among these, a composite oxide of lithium and a transition metal is preferable because it can achieve both high capacity and high cycle characteristics of a lithium secondary battery. Preferably particular lithium nickel-containing transition metal oxide in the present invention, LiNiO 2 To illustrate these, LiNi x M y O 2 ( M is Al, B, Ti, Zr, V, Cr, Mn, Fe, Co, Cu, And at least one selected from Zn, Mg, Ca and Ga, and x and y represent arbitrary numbers). As M, Co, Mn, Fe, Al, Mg, and Ti are particularly preferable. In particular, Mn alone and a combination of Co—Mn, Co—Al, and Co—Al—Mg are effective for improving thermal stability. .

Specifically, LiNi 1-ab Mn a Co b O 2 (a, b represents a number from 0 to less than 1), LiNi 1-cd Co a Al d Mg e O 2 (c, d, e is 0 or more) Represents a number less than 1), and LiNi 1-ab Mn a Co b O 2 (0 ≦ a <0.4, 0 ≦ b <0.4), LiNi 1-cd Co a Al d Mg e O 2 (0 ≦ c <0.3, 0 ≦ d <0.1, 0 ≦ e <0.05) is preferable, especially LiNi 1/3 Mn 1/3 Co 1/3 O 2 , LiNi 0.5 Mn 0.3 Co 0.2 O 2 , LiNi 0.5 Mn 0.5 O 2 , LiNi 0.85 Co 0.10 Al 0.05 O 2 , LiNi 0.85 Co 0.10 Al 0.03 Mg 0.02 O 2 are preferred.

Furthermore, the surface of the composite oxide of transition metal and lithium described above is oxidized with metals such as Al, B, Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mg, Ca, and Ga. It is preferable to coat with an object because the oxidation reaction of the solvent at a high voltage is suppressed. Of these, Al 2 O 3 , TiO 2 , ZrO 2 , and MgO are particularly preferable because they have high strength and exhibit a stable coating effect.

In addition, any one of these positive electrode active materials may be used alone, or two or more thereof may be used in any combination and ratio.
The specific surface area of the positive electrode active material is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.1 m 2 / g or more, preferably 0.2 m 2 / g or more, and usually 10 m 2 / g. Hereinafter, it is preferably 5.0 m 2 / g or less, more preferably 3.0 m 2 / g or less. If the specific surface area is too small, the rate characteristics and capacity may be reduced. If the specific surface area is too large, the positive electrode active material may cause an undesirable reaction with the non-aqueous electrolyte and the like, and the cycle characteristics may be deteriorated.

  Further, the average secondary particle size of the positive electrode active material is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.2 μm or more, preferably 0.3 μm or more, and usually 20 μm or less, preferably 10 μm or less. It is. If the average secondary particle size is too small, the cycle deterioration of the lithium secondary battery may be increased and handling may be difficult. If the average secondary particle size is too large, the internal resistance of the battery may be increased and output may be difficult to output.

  The thickness of the positive electrode active material layer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 1 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and most preferably 40 μm or more. Usually, it is 200 micrometers or less, Preferably it is 150 micrometers or less, More preferably, it is 100 micrometers or less. If it is too thin, it becomes difficult to apply the coating and it is difficult to ensure uniformity, and the capacity of the lithium secondary battery of the present invention may be small. On the other hand, if it is too thick, there is a risk that the rate characteristics will deteriorate.

The positive electrode active material layer is formed by, for example, slurrying the above-described positive electrode active material, a binder (binder), and various auxiliary agents as necessary with a solvent to form a coating liquid, and collecting the coating liquid. It can be manufactured by applying to the body and drying. Further, for example, the positive electrode active material described above may be roll-formed to form a sheet electrode, or compression-molded to form a pellet electrode.
Hereinafter, a case where the slurry is applied to the positive electrode current collector and dried will be described.

  The binder is not particularly limited as long as it is a material that is stable with respect to the non-aqueous solvent used in the non-aqueous electrolyte solution or the solvent used during electrode production, but weather resistance, chemical resistance, heat resistance, difficulty It is preferable to select in consideration of flammability and the like. Specific examples include inorganic compounds such as silicate and water glass, alkane polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene and polymethylstyrene. , Polymers having rings such as polyvinyl pyridine, poly-N-vinyl pyrrolidone; polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, Acrylic derivative polymers such as polyacrylamide; Fluorine resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; Polyvinyl chloride, halogen-containing polymers of polyvinylidene chloride; polyvinyl alcohol polymers such as polyvinyl alcohol such as a conductive polymer such as polyaniline can be used.

In addition, mixtures such as the above polymers, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, and the like can also be used.
Among these, preferred binders are a fluororesin and a CN group-containing polymer.
In addition, a binder may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

  When a resin is used as the binder, the weight average molecular weight of the resin is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 10,000 or more, preferably 100,000 or more, and usually 300. 10,000 or less, preferably 1,000,000 or less. If the molecular weight is too low, the strength of the electrode tends to decrease. On the other hand, if the molecular weight is too high, the viscosity becomes high and it may be difficult to form an electrode.

  Furthermore, the amount of the binder used is arbitrary as long as the effects of the present invention are not significantly impaired. However, the positive electrode active material (in the case of use in the negative electrode, the negative electrode active material. Hereinafter, the positive electrode active material and the negative electrode active material are distinguished. Without being referred to, simply referred to as “active material”) is usually 0.1 parts by weight or more, preferably 1 part by weight or more, and usually 30 parts by weight or less, preferably 20 parts by weight. It is as follows. If the amount of the binder is too small, the strength of the electrode tends to decrease, and if the amount of the binder is too large, the ionic conductivity tends to decrease.

The electrode may contain various auxiliaries as described above. Examples of the auxiliary agent include a conductive material that increases the conductivity of the electrode, and a reinforcing material that improves the mechanical strength of the electrode.
Specific examples of the conductive material are not particularly limited as long as an appropriate amount can be mixed with the active material to impart conductivity. However, carbon powders such as acetylene black, carbon black, and graphite, and various metals are usually used. Examples include fibers and foils.

As specific examples of the reinforcing material, various inorganic, organic spherical, fibrous fillers and the like can be used.
In addition, these adjuvants etc. may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.
The solvent for forming the slurry is not particularly limited in type as long as it is a solvent capable of dissolving or dispersing the active material, the binder, and auxiliary agents used as necessary. Either an aqueous solvent or an organic solvent may be used.

  Examples of the aqueous solvent include water and alcohol. On the other hand, examples of organic solvents include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran ( THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane and the like.

In addition, these solvents may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.
The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the positive electrode active material.

[1-2. Current collector]
As a material for the current collector, a known material can be arbitrarily used, but usually a metal or an alloy is used. Specifically, examples of the current collector for the positive electrode include aluminum, nickel, and SUS (stainless steel). Among these, aluminum is preferable as the positive electrode current collector. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and ratios.

  Furthermore, in order to improve the binding effect between the current collector and the active material layer formed on the surface, it is preferable that the surface of these current collectors is roughened in advance. The surface roughening method includes blasting or rolling with a rough roll, and the surface of the current collector with a wire brush equipped with abrasive cloth paper, grindstone, emery buff, steel wire, etc. to which abrasive particles are fixed. Examples thereof include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method.

Further, the shape of the current collector is arbitrary. For example, in order to reduce the weight of the battery, that is, to improve the energy density per weight, a perforated type current collector such as an expanded metal or a punching metal can be used. In this case, the weight can be freely changed by changing the aperture ratio. In addition, when a coating layer is formed on both surfaces of such a perforated current collector, the coating layer tends to be more difficult to peel due to the rivet effect of the coating layer through the hole, but the aperture ratio is too high. When it becomes high, the contact area between the coating layer and the current collector becomes small, so the adhesive strength is rather low.

  When a thin film is used as the positive electrode current collector, its thickness is arbitrary as long as the effects of the present invention are not significantly impaired, but it is usually 1 μm or more, preferably 5 μm or more, and usually 100 μm or less, preferably 50 μm or less. . If it is too thick, the capacity of the entire battery will be reduced. Conversely, if it is too thin, handling will be difficult.

[2. Negative electrode]
Any negative electrode can be used as long as it can occlude and release lithium as long as the effects of the present invention are not significantly impaired.
Usually, as in the case of the positive electrode, a negative electrode having a negative electrode active material layer provided on a current collector is used. Note that, similarly to the positive electrode, the negative electrode may include other layers as appropriate.

[2-1. Negative electrode active material]
The negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium ions. For example, a known negative electrode active material can be arbitrarily used. For example, carbonaceous materials such as coke, acetylene black, mesophase microbeads, and graphite; lithium metal; lithium alloys such as lithium-silicon and lithium-tin, and lithium titanate are preferably used. Among these, it is most preferable to use a carbonaceous material in terms of good cycle characteristics and safety and excellent continuous charge characteristics. In addition, a negative electrode active material may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

Further, the particle size of the negative electrode active material is arbitrary as long as the effects of the present invention are not significantly impaired, but is usually 1 μm or more, preferably 15 μm in terms of excellent battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics. These are usually 50 μm or less, preferably about 30 μm or less.
In addition, for example, those obtained by coating the above carbonaceous material with an organic substance such as pitch and then firing, those obtained by forming amorphous carbon on the surface using the CVD method, etc. It can be suitably used as a quality material. Here, organic substances used for coating include coal tar pitch from soft pitch to hard pitch; coal heavy oil such as dry distillation liquefied oil; straight heavy oil such as atmospheric residual oil and vacuum residual oil; crude oil And petroleum heavy oils such as cracked heavy oil (for example, ethylene heavy end) produced as a by-product during thermal decomposition of naphtha and the like. Moreover, what grind | pulverized the solid residue obtained by distilling these heavy oils at 200-400 degreeC to 1-100 micrometers can also be used. Furthermore, a vinyl chloride resin, a phenol resin, an imide resin, etc. can also be used.

  For example, the negative electrode active material layer can be formed into a sheet electrode by roll molding the negative electrode active material described above, or a pellet electrode by compression molding. Usually, as in the case of the positive electrode active material layer, The negative electrode active material, the binder, and, if necessary, various auxiliary agents and the like can be produced by applying a coating solution obtained by slurrying with a solvent onto a current collector and drying it. it can. As the solvent, binder, auxiliary agent and the like for forming the slurry, the same materials as those described above for the positive electrode active material can be used.

[2-2. Current collector]
As a material for the current collector of the negative electrode, a known material can be arbitrarily used. For example, a metal material such as copper, nickel, or SUS is used. Among these, copper is particularly preferable from the viewpoint of ease of processing and cost.
The negative electrode current collector is also preferably subjected to a roughening treatment in advance, as with the positive electrode current collector.
Further, like the positive electrode, the shape of the current collector is also arbitrary, and a perforated current collector such as expanded metal or punching metal can also be used. Moreover, the preferable thickness when using a thin film as a current collector is the same as that of the positive electrode.

[3. Spacer]
In order to prevent a short circuit, a spacer is usually interposed between the positive electrode and the negative electrode. The material and shape of the spacer are not particularly limited, but those that are stable with respect to the non-aqueous electrolyte described above, have excellent liquid retention properties, and can reliably prevent short-circuiting between electrodes are preferable.
As a material for the spacer, for example, polyolefin such as polyethylene and polypropylene, polytetrafluoroethylene, polyethersulfone and the like can be used, and polyolefin is preferable.
The spacer is preferably porous. In this case, the non-aqueous electrolyte is used by impregnating a porous spacer.

  The thickness of the spacer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 1 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and usually 50 μm or less, preferably 40 μm or less, more preferably. Is 30 μm or less. If the spacer is too thin, the insulation and mechanical strength may be deteriorated. If the spacer is too thick, not only the battery performance such as rate characteristics may be deteriorated, but also the energy density of the entire battery may be reduced. .

  Further, when a porous film is used as the spacer, the porosity of the spacer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 20% or more, preferably 35% or more, more preferably 45% or more. It is usually 90% or less, preferably 85% or less, and more preferably 75% or less. If the porosity is too small, the membrane resistance increases and the rate characteristics tend to deteriorate. On the other hand, if it is too large, the mechanical strength of the film tends to decrease and the insulating property tends to decrease.

  Further, when a porous film is used as the spacer, the average pore diameter of the spacer is arbitrary as long as the effect of the present invention is not significantly impaired, but it is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.8. It is 05 μm or more. If it is too large, a short circuit is likely to occur, and if it is too small, the film resistance increases and the rate characteristics may deteriorate.

[4. Assembly of secondary battery]
The lithium secondary battery of the present invention is manufactured by assembling the above-described non-aqueous electrolyte solution according to the present invention, a positive electrode, a negative electrode, and a spacer used as necessary into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary. Furthermore, the shape of the lithium secondary battery of the present invention is not particularly limited, and can be appropriately selected from various shapes generally employed according to the application. For example, a coin-type battery, a cylindrical battery, a square battery, etc. are raised. The method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples and comparative examples, and may be arbitrarily set without departing from the gist of the present invention. It can be implemented with deformation.
<Explanation of test operation>
[Production of positive electrode]
94 parts by weight of lithium nickel cobalt manganese composite oxide (LiNi 1/3 Co 1/3 Mn 1/3 O 2 ) which is a positive electrode active material, 3 parts by weight of polyvinylidene fluoride (hereinafter referred to as “PVdF” as appropriate) and acetylene black 3 parts by weight was mixed, and N-methylpyrrolidone added to form a slurry was applied to both sides of a current collector made of aluminum and dried to obtain a positive electrode.

[Manufacture of negative electrode]
A negative electrode was obtained by mixing 94 parts by weight of graphite powder, which is a negative electrode active material, and 6 parts by weight of PVdF, adding N-methylpyrrolidone into a slurry, and coating and drying on one side of a current collector made of copper. .
[Manufacture of lithium secondary batteries]
The positive electrode, the negative electrode, and the polyethylene separator were laminated in the order of the negative electrode, the separator, the positive electrode, the separator, and the negative electrode. The battery element thus obtained was wrapped in a cylindrical aluminum laminate film, injected with an electrolyte described later, and then vacuum sealed to produce a sheet-like non-aqueous electrolyte secondary battery. Furthermore, in order to improve the adhesion between the electrodes, the sheet-like battery was sandwiched between glass plates and pressurized.

[Capacity evaluation test]
In a constant temperature bath at 25 ° C., the battery was constant current-constant voltage charged (hereinafter referred to as “CCCV charge” as appropriate) to 4.1 V with a current corresponding to 0.2 C, and then discharged to 3 V at 0.2 C. This was repeated three times to form an initial formation. Subsequently, after CCCV charge to 4.4V at 0.2C, it discharged again to 3V at 0.2C, and the initial discharge capacity was obtained. The cut current during charging was set to 0.05C.
Here, 1C represents a current value for discharging the reference capacity of the battery in one hour, and for example, 0.2C represents a current value of 1/5 thereof.

[Continuous charging characteristics evaluation test]
The battery for which the capacity evaluation was completed was placed in a constant temperature bath at 60 ° C., charged at a constant current to 4.45 V at 0.2 C, and switched to constant voltage charging when it reached 4.45 V. After charging for 7 days, stop energization, take out the battery, discharge at 25 ° C to 3V at 0.2C, then charge to CCCV to 0.2V at 0.2C (cut current during charging is 0.05C), and then discharged to 3V at 0.2C to determine the discharge capacity after continuous charging. Further, the discharge capacity recovery rate before and after the continuous charge test was obtained by the following formula.

[Equation 1]
Capacity recovery rate (%) = discharge capacity after continuous charge (mAh / g) / initial discharge capacity (mAh / g)

<Example 1>
1 mol of LiPF 6 as an electrolyte is mixed in a mixed solvent (mixing volume ratio 10: 10: 70: 10) with fluoroethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). Non-aqueous solution by adding citraconic anhydride and 1,3-propane sultone (PS) to 0.2 wt% and 1 wt%, respectively, with respect to the total weight of the electrolyte. An electrolyte was used.
Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test and a continuous charge characteristic evaluation test were performed. The results are shown in Table 1.

<Example 2>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that itaconic anhydride was used instead of citraconic anhydride. The results are shown in Table 1.

<Example 3>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that maleic anhydride was used instead of citraconic anhydride. The results are shown in Table 1.

<Example 4>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that phenylsuccinic anhydride was used instead of citraconic anhydride. The results are shown in Table 1.

<Example 5>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that succinic anhydride was used instead of citraconic anhydride. The results are shown in Table 1.

<Example 6>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that 1,3-propene sultone (PRS) was used instead of 1,3-propane sultone. The results are shown in Table 1.

<Example 7>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that dimethyl sulfone (DMS) was used instead of 1,3-propane sultone. The results are shown in Table 1.

<Example 8>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that the amount of citraconic anhydride added was 0.1% by weight. The results are shown in Table 1.

<Example 9>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that the amount of citraconic anhydride added was 0.5% by weight. The results are shown in Table 1.

<Example 10>
LiPF 6 as an electrolyte is dissolved at a rate of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) and vinylene carbonate (VC) (mixing volume ratio 30: 69: 1). The same as Example 1 except that acid and 1,3-propane sultone (PS) were added so as to be 0.2% by weight and 1% by weight, respectively, with respect to the total weight of the electrolytic solution to obtain a non-aqueous electrolytic solution. A secondary battery was fabricated and evaluated. The results are shown in Table 1.

<Comparative Example 1>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that citraconic anhydride was not added. The results are shown in Table 1.

<Comparative example 2>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that 1,3-propane sultone was not added. The results are shown in Table 1.

<Comparative Example 3>
A secondary battery was prepared and evaluated in the same manner as in Example 1 except that the amount of citraconic anhydride added was 2% by weight. The results are shown in Table 1.

<Comparative Example 4>
In a mixed solvent (mixing volume ratio 30:70) with ethylene carbonate (EC) and dimethyl carbonate (DMC), LiPF 6 as an electrolyte is dissolved at a rate of 1 mol / L, and citraconic anhydride and 1,3-propane are further dissolved. A secondary battery was fabricated in the same manner as in Example 1 except that sultone (PS) was added to 0.2 wt% and 1 wt%, respectively, with respect to the total weight of the electrolyte solution to obtain a non-aqueous electrolyte solution. A continuous charge characteristic evaluation test was conducted. The results are shown in Table 1.

<Comparative Example 5>
A secondary battery was produced in the same manner as in Comparative Example 4 except that citraconic anhydride was not added, and a continuous charge characteristic evaluation test was performed. The results are shown in Table 1.

  From Table 1, when the non-aqueous electrolyte solution of Examples 1 to 9 according to the present invention is used, when the cyclic acid anhydride is not added (Comparative Example 1), the S = O group-containing organic compound is added. It can be seen that the capacity retention ratio before and after the continuous charge is greatly improved compared to the case where the cyclic acid anhydride is added in excess of 1% by weight (Comparative Example 3). Moreover, from Comparative Examples 4-5, in the case of the electrolyte solution which does not contain the cyclic carbonate which does not have both a fluorine substituent and a carbon-carbon unsaturated bond, both a cyclic acid anhydride and a S = O group containing organic compound It can be seen that there is no effect even if the carbon is added, and the capacity retention rate before and after continuous charging is improved when a carbonate containing a carbon-carbon unsaturated bond is further contained (Example 10).

  The use of the lithium secondary battery of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CD players, and mini disc players. , Walkie-talkies, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, watches, strobes, cameras, etc.

Claims (8)

  1. In a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous organic solvent, the non-aqueous organic solvent contains a cyclic carbonate having a fluorine substituent and / or a carbon-carbon unsaturated bond, and the non-aqueous electrolyte solution further includes: A non-aqueous electrolytic solution containing 0.001 to 0.5 wt% and 0.001 to 10 wt% of a cyclic acid anhydride and an S═O group-containing organic compound with respect to the weight of the non-aqueous electrolytic solution, respectively.
  2. The non-aqueous electrolyte solution according to claim 1, wherein the cyclic acid anhydride is a cyclic acid anhydride having a carbon-carbon unsaturated bond.
  3. The non-aqueous electrolyte solution according to claim 1 or 2, wherein the cyclic acid anhydride is a cyclic acid anhydride having a molecular weight of 250 or less.
  4. 4. The organic compound containing an S═O group is at least one selected from the group consisting of sulfoxides, sulfites, sulfones, sulfonates, sultones, and sulfates. Non-aqueous electrolyte.
  5. The cyclic acid anhydride and S = O group-containing organic compound are contained in an amount of 0.001 to 0.25% by weight and 0.001 to 5% by weight, respectively, based on the weight of the nonaqueous electrolytic solution. The non-aqueous electrolyte solution described in 1.
  6. The non-aqueous electrolyte solution according to any one of claims 1 to 5, wherein the fluorine-substituted cyclic carbonate is a carbonate represented by the general formula (1).
    (Wherein, in each of R 1 to R 4 independently represents a hydrogen atom, a fluorine atom, an alkyl group or a fluorine-substituted alkyl group having 1 to 4 carbon atoms, 1 to 4 carbon atoms, the R 1 to R 4 At least one is a fluorine atom or a C1-C4 fluorine-substituted alkyl group.)
  7. The cyclic carbonate having a carbon-carbon unsaturated bond is at least one selected from the group consisting of vinylene carbonate derivatives and vinylethylene carbonate derivatives, according to any one of claims 1 to 6. Non-aqueous electrolyte.
  8. A non-aqueous electrolyte battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution is the non-aqueous electrolyte solution according to any one of claims 1 to 7. A lithium secondary battery characterized by that.
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