JP6035776B2 - Non-aqueous electrolyte and lithium secondary battery using the same - Google Patents

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 isocyanate as an auxiliary agent. Patent Document 1 discloses that storage characteristics at 60 ° C. are improved by using an electrolytic solution containing a compound having an isocyanato group represented by 1,3-diisocyanato-4-methylbenzene. Patent Document 2 discloses that cycle characteristics are improved by using an electrolyte containing an isocyanate such as hexamethylene diisocyanate. Patent Document 3 discloses that cycle characteristics are improved by using an electrolytic solution containing a chain isocyanate and an unsaturated cyclic carbonate.

  Patent Document 4 discloses that the use of an electrolyte containing a diisocyanate such as hexamethylene diisocyanate suppresses the storage gas and improves the cycle characteristics. Patent Document 5 discloses that cycle characteristics and rate characteristics are improved by using a silicon alloy negative electrode and using an electrolytic solution containing diisocyanate and a fluorinated cyclic carbonate.

JP 2002-8719 A JP 2005-259641 A JP 2006-164759 A JP 2007-242411 A WO2010 / 021236

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. A number of methods for improving these characteristics have been proposed, but there are few reported examples that can withstand practical use. When the present inventors examined, the technique currently disclosed by patent documents 1-5 was inadequate to make the various characteristics in a high temperature storage test compatible.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a lithium secondary battery in which various characteristics in a high-temperature storage test are greatly improved.

As a result of intensive studies to solve the above problems, the inventors of the present invention contain a chain carboxylic acid ester in an amount of 5 to 70% by mass with respect to the mass of the nonaqueous electrolytic solution, and two or more isocyanate groups. It has been found that various characteristics such as cycle characteristics, storage characteristics and continuous charge characteristics, in particular, various characteristics such as high temperature storage characteristics can be improved by using a non-aqueous electrolyte containing a compound having the present invention, and the present invention has been completed.

That is, the gist of the present invention is as follows.
A non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous organic solvent, the non-aqueous electrolyte solution containing a chain carboxylic acid ester in an amount of 5 to 70% by mass with respect to the mass of the non-aqueous electrolyte solution, and unsaturated
A non-aqueous electrolyte solution containing 0.001 to 10% by mass of cyclic carbonate with respect to the mass of the non-aqueous electrolyte solution and further containing a compound having two or more isocyanate groups (provided that the non-aqueous electrolyte solution is hexagonal). Except when it contains methylene diisocyanate) .
At this time, it is preferable that content of the compound which has two or more isocyanate groups is 0.001-10 mass% with respect to the mass of this non-aqueous electrolyte.
The chain carboxylic acid ester is preferably a chain carboxylic acid ester represented by the following general formula (1).

R ₁ COOR ₂ (1)
(Wherein R ₁ and R ₂ are each independently a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with fluorine)
Further, it is preferable that the nonaqueous electrolytic solution mode Nofuruororin salt Moreover, and containing 0.001 to 10% by weight, based on the weight of the non-aqueous electrolyte at least one selected from difluoromethyl phosphate.

Furthermore, it is preferable that the non-aqueous electrolyte contains 0.001 to 30% by mass of a fluorine-substituted cyclic carbonate with respect to the mass of the non-aqueous electrolyte.
Another gist of the present invention resides in a lithium secondary battery including a positive electrode, a negative electrode, and the nonaqueous electrolytic solution of the present invention.

  According to the present invention, when used in a lithium secondary battery, various characteristics such as high capacity, cycle characteristics, high temperature storage characteristics, continuous charge characteristics, overcharge characteristics, and particularly high temperature storage characteristics can be greatly improved. A non-aqueous electrolyte solution and a lithium secondary battery using the electrolyte solution and improved in the above 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 and implemented 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”). It is an aqueous electrolyte solution, and the non-aqueous electrolyte solution contains a chain carboxylic acid ester (hereinafter appropriately referred to as “chain carboxylic acid ester in the present invention”) in an amount of 5 to 70% by mass with respect to the mass of the non-aqueous electrolyte solution. Furthermore, it is a non-aqueous electrolytic solution characterized by containing a compound having two or more isocyanate groups (hereinafter referred to as “compound having two or more isocyanate groups in the present invention” as appropriate).

[1. Compound having two or more isocyanate groups]
[1-1. type]
The compound having two or more isocyanate groups in the present invention is not particularly limited as long as it is a compound having two or more isocyanate groups in the molecule. Preferred are compounds having 2 or more and 4 or less isocyanato groups in the molecule, and more preferred are compounds having 2 or more and 3 or less isocyanato groups in the molecule.
As the compound having two isocyanato groups in the molecule, those represented by the following general formula (2) are preferable.

NCO-X-NCO (2)
(Wherein X is a hydrocarbon group having 1 to 16 carbon atoms which may be substituted with fluorine)
In the said General formula (2), X is a C1-C16 hydrocarbon group which may be substituted by the fluorine. The carbon number of X is preferably 2 or more, more preferably 3 or more, particularly preferably 4 or more, and is preferably 14 or less, more preferably 12 or less, particularly preferably 10 or less, and most preferably 8 or less. The type of X is not particularly limited as long as it is a hydrocarbon group. Any of an aliphatic chain alkylene group, an aliphatic cyclic alkylene group and an aromatic ring-containing hydrocarbon group may be used, but preferably an aliphatic chain alkylene group, an aliphatic cyclic alkylene group, more preferably an aliphatic chain An alkylene group;

As a specific example of a compound having two isocyanato groups in the molecule,
Linear polymethylene diisocyanates such as ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate, octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate; methyl Tetramethylene diisocyanate, dimethyltetramethylene diisocyanate, trimethyltetramethylene diisocyanate, methylhexamethylene diisocyanate, dimethylhexamethylene diisocyanate, trimethylhexamethylene diisocyanate, methyloctamethylene diisocyanate, dimethyloctane Methylene diisocyana Branched alkylene diisocyanates such as trimethyloctamethylene diisocyanate; 1,4-diisocyanato-2-butene, 1,5-diisocyanato-2-pentene, 1,5-diisocyanato-3-pentene, 1,6- Diisocyanates such as diisocyanato-2-hexene, 1,6-diisocyanato-3-hexene, 1,8-diisocyanato-2-octene, 1,8-diisocyanato-3-octene, 1,8-diisocyanato-4-octene Natoalkenes; 1,3-diisocyanato-2-fluoropropane, 1,3-diisocyanato-2,2-difluoropropane, 1,4-diisocyanato-2-fluorobutane, 1,4-diisocyanato-2,2-difluoro Butane, 1,4-diisocyanato-2,3-difluorobutane, 1,6 Diisocyanato-2-fluorohexane, 1,6-diisocyanato-3-fluorohexane, 1,6-diisocyanato-2,2-difluorohexane, 1,6-diisocyanato-2,3-difluorohexane, 1,6-diisocyanato- 2,4-difluorohexane, 1,6-diisocyanato-2,5-difluorohexane, 1,6-diisocyanato-3,3-difluorohexane, 1,6-diisocyanato-3,4-difluorohexane, 1,8- Diisocyanato-2-
Fluorooctane, 1,8-diisocyanato-3-fluorooctane, 1,8-diisocyanato-4-fluorooctane, 1,8-diisocyanato-2,2-difluorooctane, 1,8-diisocyanato-2,3-difluorooctane 1,8-diisocyanato-2,4-difluorooctane, 1,8-diisocyanato-2,5-difluorooctane, 1,8-diisocyanato-2,6-difluorooctane, 1,8-diisocyanato-2,7- Fluorine-substituted diisocyanatoalkanes such as difluorooctane; 1,2-diisocyanatocyclopentane, 1,3-diisocyanatocyclopentane, 1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane 1,4-diisocyanatocyclohexane, 1,2-bis ( Socia isocyanatomethyl) cyclohexane, 1,3-bis (isocyanatomethyl) cyclohexane, 1,4-bis (isocyanatomethyl) cyclohexane, dicyclohexylmethane-2,2'-diisocyanate, dicyclohexylmethane -2
Cycloalkane ring-containing diisocyanates such as 1,4′-diisocyanate, dicyclohexylmethane-3,3′-diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, 1,2-phenylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, tolylene-2,3-diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,5-diisocyanate, tolylene- 2,6-diisocyanate, tolylene-3,4-diisocyanate, tolylene-3,5-diisocyanate, 1,2-bis (isocyanatomethyl) benzene, 1,3-bis (isocyanatomethyl) Benzene, 1,4-bis (isocyanatomethyl) benzene, 2,4-diisocyanatobiphenyl, 2,6-diiso Anatobiphenyl, 2,2′-diisocyanatobiphenyl, 3,3′-diisocyanatobiphenyl, 4,4′-diisocyanato-2-methylbiphenyl, 4,4′-diisocyanato-3-methylbiphenyl, 4,4 '-Diisocyanato-3,3'-dimethylbiphenyl, 4,4'-diisocyanatodiphenylmethane, 4,4'-diisocyanato-2-methyldiphenylmethane, 4,4'-diisocyanato-3-methyldiphenylmethane, 4,4'-Diisocyanato-3,3'-dimethyldiphenylmethane, 1
, 5-diisocyanatonaphthalene, 1,8-diisocyanatonaphthalene, 2,3-diisocyanatonaphthalene, 1,5-bis (isocyanatomethyl) naphthalene, 1,8-bis (isocyanatomethyl) naphthalene, Aromatic ring-containing diisocyanates such as 2,3-bis (isocyanatomethyl) naphthalene;
Etc. Among these, details are given in [9. From the viewpoint of high stability of the hybrid film formed with the chain carboxylic acid ester, as detailed in the section “Mechanism”,

Linear polymethylene diisocyanates such as ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate, octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate; methyl Tetramethylene diisocyanate, dimethyltetramethylene diisocyanate, trimethyltetramethylene diisocyanate, methylhexamethylene diisocyanate, dimethylhexamethylene diisocyanate, trimethylhexamethylene diisocyanate, methyloctamethylene diisocyanate, dimethyloctane Methylene diisocyana Branched alkylene diisocyanates such as trimethyloctamethylene diisocyanate; 1,2-diisocyanatocyclopentane, 1,3-diisocyanatocyclopentane, 1,2-diisocyanatocyclohexane, 1,3-di Isocyanatocyclohexane, 1,4-diisocyanatocyclohexane, 1,2-bis (isocyanatomethyl) cyclohexane, 1,3-bis (isocyanatomethyl) cyclohexane, 1,4-bis (isocyanatomethyl) cyclohexane, dicyclohexyl Cyclohexane such as methane-2,2′-diisocyanate, dicyclohexylmethane-2,4′-diisocyanate, dicyclohexylmethane-3,3′-diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, etc. Alkane ring-containing diisocyanate Kind;
Is preferred, and

Linear polymethylene diisocyanates selected from tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate, octamethylene diisocyanate; 1,2-diisocyanatocyclopentane, 1,3-diisocyanatocyclopentane, 1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane, 1,4-diisocyanatocyclohexane, 1,2-bis (isocyanatomethyl) cyclohexane, 1,3-bis (isocyanatomethyl) cyclohexane 4-bis (isocyanatomethyl) cyclohexane, dicyclohexylmethane-2,2′-diisocyanate, dicyclohexylmethane-2,4′-diisocyanate, dicyclohexylmeta 3,3'-diisocyanate, cycloalkane ring containing diisocyanates selected from dicyclohexylmethane-4,4'-diisocyanate;
Is particularly preferred.
As the compound having three isocyanato groups in the molecule, those represented by the following general formulas (3) to (5) are preferable.

(In the formula, Y is a hydrocarbon group having 3 to 16 carbon atoms which may be substituted with fluorine)

(In the formula, Z ₁ is a hydrocarbon group having 1 to 16 carbon atoms which may be substituted with fluorine)

(In the formula, Z ₂ is a hydrocarbon group having 1 to 16 carbon atoms which may be substituted with fluorine)
In the said General formula (3), Y is a C3-C16 hydrocarbon group which may be substituted by the fluorine. The carbon number of Y is preferably 4 or more, more preferably 5 or more, particularly preferably 6 or more, and is preferably 14 or less, more preferably 12 or less, particularly preferably 10 or less, and most preferably 8 or less. The type of Y is not particularly limited as long as it is a hydrocarbon group. Any of an aliphatic chain alkylene group, an aliphatic cyclic alkylene group and an aromatic ring-containing hydrocarbon group may be used, but an aliphatic chain alkylene group and an aliphatic cyclic alkylene group are preferred.

  Specific examples of Y are as follows.

  For details, see [9. From the viewpoint of high stability of the hybrid film formed with the chain carboxylic acid ester, as detailed in the section “Mechanism”,

Is more preferable.
In the general formula (4), Z ₁ is a hydrocarbon group having 1 to 16 carbon atoms which may be substituted with fluorine. Z ₁ preferably has 2 or more carbon atoms, more preferably 3 or more, particularly preferably 4 or more, and is preferably 14 or less, more preferably 12 or less, particularly preferably 10 or less, and most preferably 8 or less. . The type of Z ₁ is not particularly limited as long as it is a hydrocarbon group. Any of an aliphatic chain alkylene group, an aliphatic cyclic alkylene group and an aromatic ring-containing hydrocarbon group may be used, but an aliphatic chain alkylene group and an aliphatic cyclic alkylene group are preferred.

In the general formula (5), Z ₂ is a hydrocarbon group having 1 to 16 carbon atoms which may be substituted with fluorine. The number of carbon atoms of Z ₂ is preferably 2 or more, more preferably 3 or more, particularly preferably 4 or more, and is preferably 14 or less, more preferably 12 or less, particularly preferably 10 or less, and most preferably 8 or less. . The type of Z ₂ is not particularly limited as long as it is a hydrocarbon group. Any of an aliphatic chain alkylene group, an aliphatic cyclic alkylene group and an aromatic ring-containing hydrocarbon group may be used, but an aliphatic chain alkylene group and an aliphatic cyclic alkylene group are preferred.
Moreover, the compound which has 2 or more of the isocyanate groups 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 compound having two or more isocyanate groups in the present invention is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.001% by mass or more with respect to the total mass of the non-aqueous electrolyte solution. 1% by mass or more, more preferably 0.2% by mass or more, and usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 2% by mass or less. When the content is within the above range, it is possible to suppress the negative electrode resistance from increasing and the capacity from decreasing, and to sufficiently exhibit the effects of the present invention.

[2. Chain carboxylic acid ester]
[2-1. type]
The chain carboxylic acid ester in the present invention is not particularly limited as long as it is a so-called chain carboxylic acid ester that does not form a cyclic structure with an ester group. It may have a substituent such as one containing a halogen atom such as chlorine, fluorine or bromine, a cyano group, an amino group, an amide group or an ether group. Among these, at least one selected from the group of compounds represented by the following general formula (1) is more preferable.

R ₁ COOR ₂ (1)
(Wherein R ₁ and R ₂ are each independently a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with fluorine)
In the formula, R ₁ and R ₂ are each independently a hydrocarbon group having 1 to 12 carbon atoms which may be fluorine-substituted, but R ₁ is preferably 1 to 1 carbon atoms which may be fluorine-substituted. 6 is a hydrocarbon group having 1 to 4 carbon atoms which may be fluorine-substituted, particularly preferably a hydrocarbon group having 1 to 3 carbon atoms which may be fluorine-substituted. And most preferably a C2-C3 hydrocarbon group not substituted with fluorine.

Specific examples of R ₁ include methyl group, ethyl group, fluoromethyl group, difluoromethyl group, trifluoromethyl group, 1-fluoroethyl group, 2-fluoroethyl group, 1,1-difluoroethyl group, 1,2 -Difluoroethyl group, 2,2-difluoroethyl group, 1,1,2-trifluoroethyl group, 1,2,2-trifluoroethyl group, 2,2,2-trifluoroethyl group, propyl group, isopropyl Group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, amyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, phenyl group, fluorophenyl group, octyl group, decyl group, dodecyl group Is mentioned. Among these, methyl group, ethyl group, fluoromethyl group, difluoromethyl group, trifluoromethyl group, 1-fluoroethyl group, 2-fluoroethyl group, 1,1-difluoroethyl group, 1,2-difluoro are preferable. Ethyl group, 2,2-difluoroethyl group, 1,1,2-trifluoroethyl group, 1,2,2-trifluoroethyl group, 2,2,2-trifluoroethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec
-Butyl group, tert-butyl group, amyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, phenyl group, fluorophenyl group, more preferably methyl group, ethyl group, fluoromethyl group, difluoromethyl group , Trifluoromethyl group, 1-fluoroethyl group, 2-fluoroethyl group, 1,1-difluoroethyl group, 1,2-difluoroethyl group, 2,2-difluoroethyl group, 1,1,2-trifluoro Ethyl group, 1,2,2-trifluoroethyl group, 2,2,2-trifluoroethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group Particularly preferably, a methyl group, an ethyl group, a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 1-fluoroethyl group, 2-fluoroethyl group, 1,1-difluoroethyl group, 1,2-difluoroethyl group, 2,2-difluoroethyl group, 1,1,2-trifluoroethyl group, 1,2,2-trifluoroethyl Group, 2,2,2-trifluoroethyl group, propyl group and isopropyl group, and most preferably ethyl group, propyl group and isopropyl group.

R ₆ is preferably a hydrocarbon group having 1 to 6 carbon atoms which may be fluorine-substituted, more preferably a hydrocarbon group having 1 to 4 carbon atoms which may be fluorine-substituted, particularly preferably. Is a hydrocarbon group having 1 to 3 carbon atoms not substituted with fluorine, and most preferably a hydrocarbon group having 1 to 2 carbon atoms not substituted with fluorine. Specific examples of R ₆ include methyl group, ethyl group, fluoromethyl group, difluoromethyl group, trifluoromethyl group, 1-fluoroethyl group, 2-fluoroethyl group, 1,1-difluoroethyl group, 1,2 -Difluoroethyl group, 2,2-difluoroethyl group, 1,1,2-trifluoroethyl group, 1,2,2-trifluoroethyl group, 2,2,2-trifluoroethyl group, propyl group, isopropyl Group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, amyl group,
Examples include pentyl group, neopentyl group, hexyl group, cyclohexyl group, phenyl group, fluorophenyl group, octyl group, decyl group, and dodecyl group. Among these, methyl group, ethyl group, fluoromethyl group, difluoromethyl group, trifluoromethyl group, 1-fluoroethyl group, 2-fluoroethyl group, 1,1-difluoroethyl group, 1,2-difluoro are preferable. Ethyl group, 2,2-difluoroethyl group, 1,1,2-trifluoroethyl group, 1,2,2-trifluoroethyl group, 2,2,2-trifluoroethyl group, propyl group, isopropyl group, n-butyl, isobutyl, sec-butyl, tert-butyl, amyl, pentyl, neopentyl, hexyl, cyclohexyl, phenyl, fluorophenyl, more preferably methyl, ethyl Group, fluoromethyl group, difluoromethyl group, trifluoromethyl group, 1-fluoroethyl group, 2-fluoroethyl group, , 1-difluoroethyl group, 1,2-difluoroethyl group, 2,2-difluoroethyl group, 1,1,2-trifluoroethyl group, 1,2,2-trifluoroethyl group, 2, 2, 2 -Trifluoroethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, particularly preferably methyl group, ethyl group,
A propyl group and an isopropyl group are most preferred, and a methyl group and an ethyl group are most preferred.
Specific examples of the chain carboxylic esters represented by the general formula (1) include methyl acetate, fluoromethyl acetate, difluoromethyl acetate, trifluoromethyl acetate, ethyl acetate, 1-fluoroethyl acetate, 2-fluoroethyl acetate, 1,1-difluoroethyl acetate, 1,2-difluoroethyl acetate, 2,2-difluoroethyl acetate, 1,1,2-trifluoroethyl acetate, 1,2,2-trifluoroacetic acid Ethyl, 2,2,2-trifluoroethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, tert-butyl acetate, cyclohexyl acetate, phenyl acetate, 2-acetate
Acetic esters such as fluorophenyl, 3-fluorophenyl acetate, 4-fluorophenyl acetate, cyclohexyl acetate, octyl acetate, decyl acetate, dodecyl acetate,
Methyl monofluoroacetate, fluoromethyl monofluoroacetate, difluoromethyl monofluoroacetate, trifluoromethyl monofluoroacetate, ethyl monofluoroacetate, 1-fluoroethyl monofluoroacetate, 2-fluoroethyl monofluoroacetate, monofluoroacetic acid 1, 1-difluoroethyl, 1,2-difluoroethyl monofluoroacetate, 2,2-difluoroethyl monofluoroacetate, 1,1,2-trifluoroethyl monofluoroacetate, 1,2,2-trifluoroethyl monofluoroacetate 2,2,2-trifluoroethyl monofluoroacetate, n-propyl monofluoroacetate, isopropyl monofluoroacetate, n-butyl monofluoroacetate, isobutyl monofluoroacetate, sec-butyl monofluoroacetate, tert-monofluoroacetate Butyl, mono Cyclohexyl oloacetate, phenyl monofluoroacetate, 2-fluorophenyl monofluoroacetate, 3-fluorophenyl monofluoroacetate, 4-fluorophenyl monofluoroacetate, cyclohexyl monofluoroacetate, octyl monofluoroacetate, decyl monofluoroacetate, monofluoro Monofluoroacetic acid esters such as dodecyl acetate,

Methyl difluoroacetate, fluoromethyl difluoroacetate, difluoromethyl difluoroacetate, trifluoromethyl difluoroacetate, ethyl difluoroacetate, 1-fluoroethyl difluoroacetate, 2-fluoroethyl difluoroacetate, 1,1-difluoroethyl difluoroacetate, difluoroacetic acid 1 , 2-difluoroethyl, 2,2-difluoroethyl difluoroacetate, 1,1,2-trifluoroethyl difluoroacetate, 1,2,2-trifluoroethyl difluoroacetate, 2,2,2-trifluoroethyl difluoroacetate , N-propyl difluoroacetate, isopropyl difluoroacetate, n-butyl difluoroacetate, isobutyl difluoroacetate, sec-butyl difluoroacetate, tert-butyl difluoroacetate, cyclohexyl difluoroacetate, difluoroacetic acid Eniru, difluoro acetic acid 2-fluorophenyl, difluorophenyl acetic acid 3-fluorophenyl, difluorophenyl acetic acid 4-fluorophenyl, difluorophenyl cyclohexyl acetate, difluoromethyl octyl acetate, difluoro acetic acid decyl, difluoro acetic esters such difluoroacetate dodecyl ethers,

Methyl trifluoroacetate, fluoromethyl trifluoroacetate, difluoromethyl trifluoroacetate, trifluoromethyl trifluoroacetate, ethyl trifluoroacetate, 1-fluoroethyl trifluoroacetate, 2-fluoroethyl trifluoroacetate, trifluoroacetic acid 1, 1-difluoroethyl, 1,2-difluoroethyl trifluoroacetate, 2,2-difluoroethyl trifluoroacetate, 1,1,2-trifluoroethyl trifluoroacetate, 1,2,2-trifluoroethyl trifluoroacetate , 2,2,2-trifluoroethyl trifluoroacetate, n-propyl trifluoroacetate, isopropyl trifluoroacetate, n-butyl trifluoroacetate, isobutyl trifluoroacetate, sec-butyl trifluoroacetate, tert-trifluoroacetic acid Butyl, trif Cyclohexyl oloacetate, phenyl trifluoroacetate, 2-fluorophenyl trifluoroacetate, 3-fluorophenyl trifluoroacetate, 4-fluorophenyl trifluoroacetate, cyclohexyl trifluoroacetate, octyl trifluoroacetate, decyl trifluoroacetate, trifluoro Trifluoroacetic acid esters such as dodecyl acetate,

Methyl propionate, fluoromethyl propionate, difluoromethyl propionate, trifluoromethyl propionate, ethyl propionate, 1-fluoroethyl propionate, 2-fluoroethyl propionate, 1,1-difluoroethyl propionate, propionic acid 1 , 2-difluoroethyl, 2,2-difluoroethyl propionate, 1,1,2-trifluoroethyl propionate, 1,2,2-trifluoroethyl propionate, 2,2,2-trifluoroethyl propionate , N-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, sec-butyl propionate, tert-butyl propionate, cyclohexyl propionate, phenyl propionate, 2-fluorophenyl propionate Propionic acid 3-fluorophenyl, propionic acid 4-fluorophenyl, cyclohexyl propionate, octyl propionate, decyl propionate, propionic acid esters such as dodecyl propionate,

Methyl butyrate, fluoromethyl butyrate, difluoromethyl butyrate, trifluoromethyl butyrate, ethyl butyrate, 1-fluoroethyl butyrate, 2-fluoroethyl butyrate, 1,1-difluoroethyl butyrate, 1,2-difluoroethyl butyrate, 2, butyric acid 2, 2-difluoroethyl, 1,1,2-trifluoroethyl butyrate, 1,2,2-trifluoroethyl butyrate, 2,2,2-trifluoroethyl butyrate, n-propyl butyrate, isopropyl butyrate, n-butyl butyrate , Isobutyl butyrate, sec-butyl butyrate, tert-butyl butyrate, cyclohexyl butyrate, phenyl butyrate, 2-butyric acid
Butyrate esters such as fluorophenyl, 3-fluorophenyl butyrate, 4-fluorophenyl butyrate, cyclohexyl butyrate, octyl butyrate, decyl butyrate, dodecyl butyrate,

Cyclohexanecarboxylic acid methyl, cyclohexanecarboxylic acid fluoromethyl, cyclohexanecarboxylic acid difluoromethyl, cyclohexanecarboxylic acid trifluoromethyl, cyclohexanecarboxylic acid ethyl, cyclohexanecarboxylic acid 1-fluoroethyl, cyclohexanecarboxylic acid 2-fluoroethyl, cyclohexanecarboxylic acid 1, 1-difluoroethyl, cyclohexanecarboxylic acid 1,2-difluoroethyl, cyclohexanecarboxylic acid 2,2-difluoroethyl, cyclohexanecarboxylic acid 1,1,2-trifluoroethyl, cyclohexanecarboxylic acid 1,2,2-trifluoroethyl , Cyclohexanecarboxylic acid 2,2,2-trifluoroethyl, cyclohexanecarboxylic acid n-propyl, cyclohexanecarboxylic acid isopropyl , Cyclohexanecarboxylic acid n-butyl, cyclohexanecarboxylic acid isobutyl, cyclohexanecarboxylic acid sec-butyl, cyclohexanecarboxylic acid tert-butyl, cyclohexanecarboxylic acid cyclohexyl, cyclohexanecarboxylic acid phenyl, cyclohexanecarboxylic acid 2-fluorophenyl, cyclohexanecarboxylic acid 3- Cyclohexanecarboxylic acid esters such as fluorophenyl, cyclofluorocarboxylic acid 4-fluorophenyl, cyclohexyl cyclohexanecarboxylate, octyl cyclohexanecarboxylate, decyl cyclohexanecarboxylate, dodecyl cyclohexanecarboxylate,

Methyl benzoate, fluoromethyl benzoate, difluoromethyl benzoate, trifluoromethyl benzoate, ethyl benzoate, 1-fluoroethyl benzoate, 2-fluoroethyl benzoate, 1,1-difluoroethyl benzoate, benzoic acid 1 , 2-difluoroethyl, 2,2-difluoroethyl benzoate, 1,1,2-trifluoroethyl benzoate, 1,2,2-trifluoroethyl benzoate, 2,2,2-trifluoroethyl benzoate N-propyl benzoate, isopropyl benzoate, n-butyl benzoate, isobutyl benzoate, sec-butyl benzoate, tert-butyl benzoate, cyclohexyl benzoate, phenyl benzoate, 2-fluorophenyl benzoate, benzoic acid 3-fluorophenyl, 4-fluorophenyl benzoate, cyclohexyl benzoate, Kosan octyl, decyl benzoate, benzoic acid esters such as benzoic acid dodecyl,

Etc. Among these, methyl acetate, fluoromethyl acetate, difluoromethyl acetate, trifluoromethyl acetate, ethyl acetate, 1-fluoroethyl acetate, 2-fluoroethyl acetate, 1,1-difluoroethyl acetate, 1, 2-difluoroethyl, 2,2-difluoroethyl acetate, 1,1,2-trifluoroethyl acetate, 1,2,2-trifluoroethyl acetate, 2,2,2-trifluoroethyl acetate, n-propyl acetate , Acetate esters such as isopropyl acetate, n-butyl acetate, isobutyl acetate, sec-butyl acetate, tert-butyl acetate,

Methyl monofluoroacetate, fluoromethyl monofluoroacetate, difluoromethyl monofluoroacetate, trifluoromethyl monofluoroacetate, ethyl monofluoroacetate, 1-fluoroethyl monofluoroacetate, 2-fluoroethyl monofluoroacetate, monofluoroacetic acid 1, 1-difluoroethyl, 1,2-difluoroethyl monofluoroacetate, 2,2-difluoroethyl monofluoroacetate, 1,1,2-trifluoroethyl monofluoroacetate, 1,2,2-trifluoroethyl monofluoroacetate 2,2,2-trifluoroethyl monofluoroacetate, n-propyl monofluoroacetate, isopropyl monofluoroacetate, n-butyl monofluoroacetate, isobutyl monofluoroacetate, sec-butyl monofluoroacetate, tert-monofluoroacetate Butyl etc. Fluoro acetates,

Difluoroacetic acid methyl, difluoroacetic acid fluoromethyl, difluoroacetic acid difluoromethyl, difluoroacetic acid trifluoromethyl, difluoroacetic acid ethyl, difluoroacetic acid 1-
Fluoroethyl, 2-fluoroethyl difluoroacetate, 1,1-difluoroethyl difluoroacetate, 1,2-difluoroethyl difluoroacetate, 2,2-difluoroethyl difluoroacetate, 1,1,2-trifluoroethyl difluoroacetate, difluoroacetate 1,2,2-trifluoroethyl acetate, 2,2,2-trifluoroethyl difluoroacetate, n-propyl difluoroacetate, isopropyl difluoroacetate, n-butyl difluoroacetate, isobutyl difluoroacetate, sec-butyl difluoroacetate, difluoro Difluoroacetic acid esters such as tert-butyl acetate;

Methyl trifluoroacetate, fluoromethyl trifluoroacetate, difluoromethyl trifluoroacetate, trifluoromethyl trifluoroacetate, ethyl trifluoroacetate, 1-fluoroethyl trifluoroacetate, 2-fluoroethyl trifluoroacetate, trifluoroacetic acid 1, 1-difluoroethyl, 1,2-difluoroethyl trifluoroacetate, 2,2-difluoroethyl trifluoroacetate, 1,1,2-trifluoroethyl trifluoroacetate, 1,2,2-trifluoroethyl trifluoroacetate , 2,2,2-trifluoroethyl trifluoroacetate, n-propyl trifluoroacetate, isopropyl trifluoroacetate, n-butyl trifluoroacetate, isobutyl trifluoroacetate, sec-butyl trifluoroacetate, tert-trifluoroacetic acid Toluene such as butyl Fluoro acetates,

Methyl propionate, fluoromethyl propionate, difluoromethyl propionate, trifluoromethyl propionate, ethyl propionate, 1-fluoroethyl propionate, 2-fluoroethyl propionate, 1,1-difluoroethyl propionate, propionic acid 1 , 2-difluoroethyl, 2,2-difluoroethyl propionate, 1,1,2-trifluoroethyl propionate, 1,2,2-trifluoroethyl propionate, 2,2,2-trifluoroethyl propionate Propionates such as n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, sec-butyl propionate, tert-butyl propionate,

Methyl butyrate, fluoromethyl butyrate, difluoromethyl butyrate, trifluoromethyl butyrate, ethyl butyrate, 1-fluoroethyl butyrate, 2-fluoroethyl butyrate, 1,1-difluoroethyl butyrate, 1,2-difluoroethyl butyrate, 2, butyric acid 2, 2-difluoroethyl, 1,1,2-trifluoroethyl butyrate, 1,2,2-trifluoroethyl butyrate, 2,2,2-trifluoroethyl butyrate, n-propyl butyrate, isopropyl butyrate, n-butyl butyrate , Butyric acid esters such as isobutyl butyrate, sec-butyl butyrate, tert-butyl butyrate,
Especially preferred are as follows:

Acetic esters such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, monofluoroacetic esters such as methyl monofluoroacetate, ethyl monofluoroacetate, n-propyl monofluoroacetate, isopropyl monofluoroacetate, difluoroacetic acid Difluoroacetates such as methyl, ethyl difluoroacetate, n-propyl difluoroacetate, isopropyl difluoroacetate, trifluoroacetates such as methyl trifluoroacetate, ethyl trifluoroacetate, n-propyl trifluoroacetate, isopropyl trifluoroacetate , Propionates such as methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, butyrate such as methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate Le acids,
As the most preferable one,
Examples include methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate.

[2-2. composition]
The content of the chain carboxylic acid ester in the present invention is 5% by mass or more, preferably 7% by mass or more, more preferably 10% by mass or more, and particularly preferably 15% by mass or more with respect to the whole non-aqueous electrolyte solution. Yes, and most preferably 20% by mass or more. Moreover, it is 70 mass% or less, Preferably it is 60 mass% or less, More preferably, it is 50 mass% or less, Most preferably, it is 45 mass% or less, Most preferably, it is 40 mass% or less.
When the content of the carboxylic acid ester is within the above range, the effects of the present invention can be sufficiently exerted, and a reduction in high load capacity due to a decrease in conductivity is suppressed.

[3. Non-aqueous organic solvent other than chain carboxylic acid ester]
The nonaqueous electrolytic solution in the present invention contains a chain carboxylic acid ester as described above, but there is no particular limitation on the other solvent, and a known organic solvent can be used. Examples thereof include cyclic carbonates, chain carbonates, cyclic esters (lactone compounds), chain ethers, cyclic ethers, sulfur-containing organic solvents, nitrogen-containing organic solvents, and the like. Of these, cyclic carbonates, chain carbonates, cyclic esters, chain ethers, cyclic ethers, and sulfur-containing organic solvents are preferred as solvents that exhibit high ionic conductivity.

  Examples of the cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, dimethylethylene carbonate, diethylethylene carbonate, monopropylethylene carbonate, dipropylethylene 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 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.
Specific examples of the sulfur-containing organic solvent include sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, methyl phenyl sulfone, diphenyl sulfone, and 1,3-propane sultone. Of these, sulfolane is preferred.

In the non-aqueous organic solvent in the present invention, as the non-aqueous organic solvent other than the chain carboxylic acid ester, one type may be used alone, or two or more types may be used in any combination and ratio, It is preferable to use a mixture of two or more solvents.
In the non-aqueous organic solvent in the present invention, the content of the non-aqueous organic solvent other than the chain carboxylic acid ester is not particularly limited. Cyclic carbonates and chain carbonates are preferably used as non-aqueous organic solvents other than chain carboxylic acid esters. The content of the cyclic carbonate is usually 10% by mass or more, preferably 15% by mass or more, more preferably 20% by mass or more, and usually 50% by mass or less, preferably 40% by mass or less. More preferably, it is 35 mass% or less.

[4. 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. Specific examples include the following.
For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAlF ₄ , LiSbF ₆ , LiTaF ₆ , LiWF _{7 and} other inorganic lithium salts; LiWOF _{5 and} other lithium tungstates; HCO ₂ Li, CH ₃ CO ₂ Li, CH ₂ FCO ₂ Li, CHF ₂ CO ₂ Li, CF ₃ CO ₂ Li, CF ₃ CH ₂ CO ₂ Li, CF ₃ CF ₂ CO ₂ Li, CF ₃ CF ₂ CF ₂ CO ₂ Li, CF ₃ CF ₂ CF ₂ CF ₂ CO ₂ Lithium carboxylate such as Li; FSO ₃ Li, CH ₃ SO ₃ Li, CH ₂ FSO ₃ Li, CHF ₂ SO ₃ Li, CF ₃ SO ₃ Li, CF ₃ CF ₂ SO ₃ Li, CF ₃ CF ₂ CF Sulfonic acid lithium salts such as ₂ SO ₃ Li, CF ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li; LiN (FCO) ₂ , LiN (FCO) (FSO ₂ ), LiN (FSO ₂ ) ₂ , LiN (FSO ₂ ) (CF ₃ SO ₂ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Lithium imide salts such as lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) Lithium methide salts such as LiC (FSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ ; lithium oxalatoborate such as lithium difluorooxalatoborate and lithium bis (oxalato) borate Salts; lithium tetrafluorooxalatophosphate, lithium difluorobis (oxa Lato) phosphates, lithium oxalatophosphate salts such as lithium tris (oxalato) phosphate; other LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (CF ₃ SO ₂ ) ₂ , LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiBF ₃ C ₃ F ₇ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , And fluorine-containing organolithium salts such as LiBF ₂ (CF ₃ SO ₂ ) ₂ and LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ .

Among them, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiTaF ₆ , FSO ₃ Li, CF ₃ SO ₃ Li, LiN (FSO ₂ ) ₂ , LiN (FSO ₂ ) (CF ₃ SO ₂ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiC (FSO ₂ ) ₃ , LiC (CF _{3 SO 2) 3, LiC (C} 2 F 5 SO 2) 3, lithium Bisuo Kisara oxalatoborate, lithium difluoro oxalatoborate, lithium tetrafluoro-oxa Lato phosphate, lithium difluoro bis oxa Lato _phosphate, LiBF ₃ CF _3, LiBF ₃ C ₂ F ₅ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) _{3 and the} like are particularly preferable because they have an effect of improving output characteristics, high-rate charge / discharge characteristics, high-temperature storage characteristics, cycle characteristics, and the like.

These lithium salts may be used alone or in combination of two or more. A preferable example in the case of using two or more kinds in combination is a combination of LiPF ₆ and LiBF ₄ , LiPF ₆ and FSO ₃ Li, and the like, which has an effect of improving load characteristics and cycle characteristics. In this case, the concentration of LiBF ₄ or FSO ₃ Li with respect to 100% by mass of the entire non-aqueous electrolyte solution is not limited as long as it does not significantly impair the effects of the present invention. For normal, 0
. It is 01 mass% or more, preferably 0.1 mass% or more, and is usually 30 mass% or less, preferably 20 mass% or less.

Another example is the combined use of an inorganic lithium salt and an organic lithium salt, and the combined use of both has the effect of suppressing deterioration due to high-temperature storage. As the organic lithium salt, CF ₃ SO ₃ Li, LiN (FSO ₂ ) ₂ , LiN (FSO ₂ ) (CF ₃ SO ₂ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiC (FSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluorooxalate phosphate, lithium difluorobisoxalatophosphate, LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiPF ₃ (CF ₃ ) ₃ LiPF ₃ (C ₂ F ₅ ) ₃ or the like is preferable. In this case, the ratio of the organic lithium salt to 100% by mass of the entire non-aqueous electrolyte is usually 0.1% by mass or more, preferably 0.5% by mass or more, and usually 30% by mass or less, preferably 20% by mass. % Or less.

  The concentration of these lithium salts in the non-aqueous electrolyte solution is not particularly limited as long as the effects of the present invention are not impaired, but the electric conductivity of the electrolyte solution is in a good range, and good battery performance is ensured. Therefore, the total molar concentration of lithium in the non-aqueous electrolyte is usually 0.5 mol / L or more, preferably 0.8 mol / L or more, more preferably 1.0 mol / L or more, and further preferably 1.3 mol. / L or more, and usually 3 mol / L or less, preferably 2.5 mol / L or less, more preferably 2.0 mol / L or less. When the total molar concentration of lithium is 0.5 mol / L or more, the electric conductivity of the electrolytic solution is sufficient. On the other hand, when the concentration is 3 mol / L or less, a decrease in electric conductivity due to an increase in viscosity is prevented. .

[5. Film-forming agent]
The nonaqueous electrolytic solution according to the present invention further comprises at least one selected from unsaturated carbonate, monofluorophosphate, and difluorophosphate for the purpose of forming a film on the negative electrode and improving battery characteristics. It is preferable to contain 0.001-10 mass% with respect to the mass of this non-aqueous electrolyte. Similarly, for the purpose of forming a film on the negative electrode and improving battery characteristics, it is preferable to contain 0.001 to 30% by mass of a fluorine-substituted cyclic carbonate with respect to the mass of the nonaqueous electrolytic solution.

  The unsaturated cyclic carbonate 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 can be used. Examples of the cyclic carbonate having a carbon-carbon double bond include vinylene carbonate derivatives such as vinylene carbonate, methyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate; And vinyl ethylene carbonate derivatives such as carbonate, 1,1-divinylethylene carbonate, 1,2-divinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-phenyl-2-vinylethylene carbonate, and the like. 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. Moreover, as a cyclic carbonate having a carbon-carbon triple bond,

Especially

Is preferred.
In addition, an unsaturated cyclic carbonate 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 unsaturated cyclic carbonate is usually 3 or more, and usually 20 or less, preferably 15 or less. Further, the molecular weight of the unsaturated cyclic carbonate is usually 80 or more, and usually 250 or less, preferably 150 or less. When the carbon number and molecular weight are within the above ranges, the solubility in the electrolytic solution can be maintained and the effects of the present invention can be sufficiently exhibited.

  The content of the cyclic carbonate having an unsaturated bond is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and particularly preferably 0% with respect to the whole electrolyte solution. .3% by mass or more, usually 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less, and particularly preferably 2% by mass or less. When the content is within the above range, the effects of the present invention can be sufficiently exerted, and deterioration of the high-temperature storage characteristics can be prevented.

These cyclic carbonates having an unsaturated bond may be those containing a small amount of an antioxidant such as BHT (dibutylhydroxytoluene), BHA (butylhydroxyanisole), sodium erythorbate, propyl gallate, sodium sulfite. Good.
The monofluorophosphate and difluorophosphate are preferably sodium monofluorophosphate, lithium monofluorophosphate, potassium monofluorophosphate, sodium difluorophosphate, lithium difluorophosphate, and potassium difluorophosphate. Is particularly preferably lithium monofluorophosphate or lithium difluorophosphate.

  The content of monofluorophosphate and difluorophosphate is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and still more preferably based on the whole electrolyte solution. 0.3% by mass or more, and usually 10% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less, and further preferably 1% by mass or less. When the concentration of the monofluorophosphate and the difluorophosphate is within the above range, the effect of the present invention can be sufficiently exerted, and a decrease in capacity due to an increase in the reaction resistance of the negative electrode is prevented. be able to.

  The fluorine-substituted cyclic carbonate 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. Specific examples include fluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2- Examples include difluoro-1,2-dimethylethylene carbonate, tetrafluoroethylene carbonate, monofluoromethyl ethylene carbonate, difluoromethyl ethylene carbonate, trifluoromethyl ethylene carbonate, 2,2,2-trifluoroethyl ethylene carbonate, and the like. Among these, fluoroethylene carbonate, 1,2-difluoroethylene carbonate, and trifluoromethylethylene carbonate are more preferable from the viewpoint of achieving a good balance between improving conductivity and reducing viscosity and providing good cycle characteristics.

Moreover, a fluorine-substituted cyclic carbonate may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.
The content of the fluorine-substituted cyclic carbonate in the present invention is usually 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more with respect to the total mass of the non-aqueous electrolyte solution. More preferably, it is 0.5 mass% or more, usually 30 mass% or less, preferably 25 mass% or less, more preferably 20 mass% or less. When the content is in the above range, an effective film can be formed on the negative electrode, deterioration of high-temperature storage characteristics can be suppressed, and cost can be reduced.

[6. 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 carbonate compounds such as erythritan carbonate, spiro-bis-dimethylene carbonate, methoxyethyl-methyl carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, phenylmaleic anhydride, citraconic anhydride, Carboxylic anhydrides such as glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride and phenylsuccinic anhydride; 2,4,8,10-tetraoxa Spiro compounds such as spiro [5.5] undecane, 3,9-divinyl-2,4,8,10-tetraoxaspiro [5.5] undecane; 1-methyl-2-pyrrolidinone, 1-methyl-2- Piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2- Nitrogen-containing compounds such as midazolidinone, N-methylsuccinimide, succinonitrile, adiponitrile, and pimelonitrile; dimethyl sulfite, diethyl sulfite, dimethyl sulfone, diethyl sulfone, methyl methane sulfonate, ethyl methane sulfonate, methyl benzene sulfonate, ethyl benzene sulfonate, 1 , 3-propane sultone, 1,3-propene sultone, dimethyl sulfate, diethyl sulfate, 1,3,2-dioxathiolane-2,2-dioxide, 1,3,2-dioxathian-2,2-dioxide, etc. Sulfur-containing compounds: hydrocarbon compounds such as heptane, octane, nonane, decane, cycloheptane, fluorobenzene, difluorobenzene, hexafluorobenzene, t-butylbenzene, t-a Benzene, biphenyl, o-terphenyl, 2-fluorobiphenyl, 4-fluorobiphenyl, 2,4-difluorobiphenyl, fluorobenzene, 2,4-difluorobenzene, cyclohexylbenzene, diphenyl ether, 2,4-difluoroanisole, 3, And aromatic compounds such as 5-difluoroanisole and benzotrifluoride. Among these, cyclic acid anhydrides such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride and itaconic anhydride; sulfur-containing compounds such as 1,3-propane sultone and 1,3-propene sultone; succino Dinitriles such as nitrile, adiponitrile, and pimelonitrile are preferred.

These may be used alone or in combination of two or more. By adding these auxiliaries, capacity maintenance characteristics and cycle characteristics after high temperature storage can be improved. Further, the concentration of the auxiliary agent in the non-aqueous electrolytic solution is arbitrary as long as the effects of the present invention are not significantly impaired. 3% by mass or more and usually 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass 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.
These auxiliaries may contain a small amount of an antioxidant such as BHT (dibutylhydroxytoluene), BHA (butylhydroxyanisole), sodium erythorbate, propyl gallate, sodium sulfite and the like.

[7. 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 mass or more, preferably 50% by mass or more, more preferably 75% by mass or more, and usually 99.95. It is at most mass%, preferably at most 99 mass%, more preferably at most 98 mass%. When the ratio of the nonaqueous electrolytic solution is within the above range, charging / discharging efficiency and capacity are sufficient, and it is difficult to hold the electrolytic solution and easily prevent liquid leakage.

[8. 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 chain carboxylic acid ester, and a compound having two or more isocyanate groups in the present invention is further added. It can be prepared by adding.
In preparing the non-aqueous electrolyte, each raw material of the non-aqueous electrolyte, that is, lithium salt, chain carboxylic acid ester in the present invention, other non-aqueous organic solvent, compound having two or more isocyanate groups in the present invention In addition, other auxiliaries 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 addition, in this specification, ppm means the ratio on the basis of mass.

  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.

[9. mechanism]
The mechanism by which the effect of the present invention can be obtained is not clear, but is considered as follows.
A part of the isocyanate compound of the present invention reacts during the initial charging of the battery to form a film on the negative electrode. This film has a high resistance, and since the reaction proceeds by heating and becomes a higher resistance, the capacity after the storage test may be reduced. On the other hand, the chain carboxylic acid ester similarly reacts at the time of initial charge, and forms a film on the negative electrode. Although this coating has low resistance but poor thermal stability, it generates a lot of gas during the storage test.

However, when the chain carboxylic acid ester is present in the electrolytic solution, a hybrid film is formed on the negative electrode from the isocyanate compound of the present invention and the chain carboxylic acid ester during initial charging. Since this coating has a relatively low resistance and a high thermal stability, gas generation is suppressed in a high-temperature storage test, and a decrease in capacity is also improved.
[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] <Positive electrode active material>
The positive electrode active material (lithium transition metal compound) used for the positive electrode is described below.
<Lithium transition metal compound>
A lithium transition metal compound is a compound having a structure capable of desorbing and inserting Li ions, and examples thereof include sulfides, phosphate compounds, and lithium transition metal composite oxides. Examples of sulfides include compounds having a two-dimensional layered structure such as TiS ₂ and MoS ₂ , and strong compounds represented by the general formula Me _x Mo ₆ S ₈ (Me is various transition metals including Pb, Ag, and Cu). Examples thereof include a sugar compound having a three-dimensional framework structure. Examples of the phosphate compound include those belonging to the olivine structure, and are generally represented by LiMePO ₄ (Me is at least one transition metal), specifically, LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , Examples include LiMnPO ₄ . Examples of the lithium transition metal composite oxide include spinel structures capable of three-dimensional diffusion and those belonging to a layered structure capable of two-dimensional diffusion of lithium ions. Those having a spinel structure are generally expressed as LiMe ₂ O ₄ (Me is at least one transition metal), specifically, LiMn ₂ O ₄ , LiCoMnO ₄ , LiNi _0.5 Mn _1.5 O. ₄ , LiCoVO _{4 and the} like. Those having a layered structure are generally expressed as LiMeO ₂ (Me is at least one transition metal). LiCoO _{2 Specifically, LiNiO 2, LiNi 1-x} Co x O 2, LiNi 1-x-y Co x Mn y O 2, LiNi 0.5 Mn 0.5 O 2, Li 1.2 Cr 0. _{4 Mn 0.4 O 2, Li 1.2} Cr 0.4 Ti 0.4 O 2, such as LiMnO ₂ and the like.

<composition>
The lithium-containing transition metal compound is, for example, a lithium transition metal compound represented by the following composition formula (A) or (B).
1) In the case of a lithium transition metal compound represented by the following composition formula (A)

Li _{1 + x} MO ₂ (A)
However, x is usually 0 or more and 0.5 or less. M is an element composed of Ni and Mn or Ni, Mn and Co, and the Mn / Ni molar ratio is usually 0.1 or more and 5 or less. The Ni / M molar ratio is usually 0 or more and 0.5 or less. The Co / M molar ratio is usually 0 or more and 0.5 or less. In addition, the rich portion of Li represented by x may be replaced with the transition metal site M.

  In the composition formula (A), the atomic ratio of the oxygen amount is described as 2 for convenience, but there may be some non-stoichiometry. Moreover, x in the said compositional formula is the preparation composition in the manufacture stage of a lithium transition metal type compound. Usually, batteries on the market are aged after the batteries are assembled. For this reason, the Li amount of the positive electrode may be deficient with charge / discharge. In this case, x may be measured to be −0.65 or more and 1 or less when discharged to 3 V in composition analysis.

A lithium transition metal-based compound is excellent in battery characteristics when fired at a high temperature in an oxygen-containing gas atmosphere in order to enhance the crystallinity of the positive electrode active material. Further, the lithium transition metal-based compound represented by the composition formula (A) may be a solid solution with Li ₂ MO ₃ called a 213 layer, as shown in the general formula (A ′) below.

αLi ₂ MO ₃ · (1-α) LiM′O ₂ (A ′)
In the general formula, α is a number satisfying 0 <α <1.
M is at least one metallic element average oxidation number of 4 ^+, specifically, at least one metal element Mn, Zr, Ti, Ru, selected from the group consisting of Re and Pt.
M 'is at least one metallic element average oxidation number of 3 ^+, preferably, V, Mn, Fe, at least one metallic element selected from the group consisting of Co and Ni, more preferably , At least one metal element selected from the group consisting of Mn, Co and Ni.
2) A lithium transition metal compound represented by the following general formula (B).

_{Li [Li a M b Mn 2} -b-a] O 4 + δ ··· (B)
However, M is an element comprised from at least 1 sort (s) of the transition metals chosen from Ni, Cr, Fe, Co, Cu, Zr, Al, and Mg.
The value of b is usually 0.4 or more and 0.6 or less.
If the value of b is this range, the energy density per unit mass in a lithium transition metal type compound will be high.

The value of a is usually 0 or more and 0.3 or less. Moreover, a in the above composition formula is a charged composition in the production stage of the lithium transition metal compound. Usually, batteries on the market are aged after the batteries are assembled. For this reason, the Li amount of the positive electrode may be deficient with charge / discharge. In this case, a may be measured to be −0.65 or more and 1 or less when discharged to 3 V in composition analysis. When the value of a is within this range, the energy density per unit mass in the lithium transition metal compound is not significantly impaired, and good load characteristics can be obtained.
Furthermore, the value of δ is usually in the range of ± 0.5.

If the value of δ is within this range, the stability as a crystal structure is high, and the cycle characteristics and high-temperature storage of a battery having an electrode produced using this lithium transition metal compound are good.
Here, the chemical meaning of the lithium composition in the lithium nickel manganese composite oxide, which is the composition of the lithium transition metal compound, will be described in more detail below.

In order to obtain a and b in the composition formula of the lithium transition metal compound, each transition metal and lithium are analyzed with an inductively coupled plasma emission spectrometer (ICP-AES) to obtain a ratio of Li / Ni / Mn. It is calculated by the thing.
From a structural point of view, it is considered that lithium related to a is substituted for the same transition metal site. Here, due to the lithium according to a, the average valence of M and manganese becomes larger than 3.5 due to the principle of charge neutrality.
Further, the lithium transition metal based compound may be substituted with fluorine, it is expressed as _{LiMn 2 O 4-x F 2x} .

<blend>
Specific examples of the lithium transition metal compound having the above composition include, for example, Li _{1 + x} Ni _0.5 Mn _0.5 O ₂ , Li _{1 + x} Ni _0.85 Co _0.10 Al _0.05 O ₂ , Li _1+
x Ni _0.33 Mn _0.33 Co _0.33 O ₂ , Li _{1 + x} Ni _0.45 Mn _0.45 Co _0.1 O ₂ , Li _{1 + x} Mn _1.8 Al _0.2 O ₄ , Li _{1 + x} Mn _{1 .5} Ni _0.5 O ₄ and the like. These lithium transition metal compounds may be used alone or in a blend of two or more.

<Introduction of foreign elements>
Moreover, a different element may be introduce | transduced into a lithium transition metal type compound. As the different elements, B, Na, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Ru, Rh, Pd, Ag, In, Sb, Te , Ba, Ta, Mo, W, Re, Os, Ir, Pt, Au, Pb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi , N, F, S, Cl, Br, I, As, Ge, P, Pb, Sb, Si, and Sn. These foreign elements may be incorporated into the crystal structure of the lithium transition metal compound, or may not be incorporated into the crystal structure of the lithium transition metal compound, and may be a single element or compound on the particle surface or grain boundary. May be unevenly distributed.

[Positive electrode for lithium secondary battery]
The positive electrode for a lithium secondary battery is formed by forming a positive electrode active material layer containing the above-described lithium transition metal compound powder for a lithium secondary battery positive electrode material and a binder on a current collector.
The positive electrode active material layer is usually formed by mixing a positive electrode material, a binder, and a conductive material and a thickener, which are used if necessary, in a dry form into a sheet shape, and then pressing the positive electrode current collector on the positive electrode current collector. Alternatively, these materials are dissolved or dispersed in a liquid medium to form a slurry, which is applied to the positive electrode current collector and dried.

  As the material for the positive electrode current collector, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, and carbon materials such as carbon cloth and carbon paper are usually used. As for the shape, in the case of a metal material, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, a foam metal, etc., and in the case of a carbon material, a carbon plate, a carbon thin film, a carbon cylinder Etc. In addition, you may form a thin film suitably in mesh shape.

  When a thin film is used as the positive electrode current collector, its thickness is arbitrary, but a range of usually 1 μm or more and 100 mm or less is suitable. If it is thinner than the above range, the strength required for the current collector may be insufficient. On the other hand, if it is thicker than the above range, the handleability may be impaired.

The binder used in the production of the positive electrode active material layer is not particularly limited, and in the case of a coating method, any material that is stable with respect to the liquid medium used during electrode production may be used. Specific examples include polyethylene, Resin polymers such as polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, nitrocellulose, SBR (styrene butadiene rubber), NBR (acrylonitrile butadiene rubber), fluorine rubber, isoprene rubber, butadiene rubber, ethylene・ Rubber polymers such as propylene rubber, styrene / butadiene / styrene block copolymers and hydrogenated products thereof, EPDM (ethylene / propylene / diene terpolymers), styrene / ethylene / butadiene / ethylene copolymers, Styrene / isoprene styrene bromide Copolymer and its hydrogenated thermoplastic elastomeric polymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer, etc. Fluorine polymers such as soft resinous polymers, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymers, ion conductivity of alkali metal ions (especially lithium ions) And a polymer composition having the same. In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

The ratio of the binder in the positive electrode active material layer is usually 0.1% by mass or more and 80% by mass or less. If the proportion of the binder is too low, the positive electrode active material cannot be sufficiently retained and the positive electrode has insufficient mechanical strength, which may deteriorate battery performance such as cycle characteristics. Battery capacity and conductivity may be reduced.
The positive electrode active material layer usually contains a conductive material in order to increase conductivity. There are no particular restrictions on the type, but specific examples include metal materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke. And carbon materials. In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios. The proportion of the conductive material in the positive electrode active material layer is usually 0.01% by mass or more and 50% by mass or less. If the proportion of the conductive material is too low, the conductivity may be insufficient, and conversely if it is too high, the battery capacity may be reduced.

  As a liquid medium for forming a slurry, it is possible to dissolve or disperse a lithium transition metal compound powder as a positive electrode material, a binder, and a conductive material and a thickener used as necessary. If it is a solvent, there is no restriction | limiting in particular in the kind, You may use either an aqueous solvent or an organic solvent. Examples of the aqueous solvent include water and alcohol. Examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N , N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran (THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, etc. be able to. In particular, when an aqueous solvent is used, a dispersant is added together with the thickener, and a slurry such as SBR is slurried. 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 content ratio of the lithium transition metal-based compound powder as the positive electrode material in the positive electrode active material layer is usually 10% by mass or more and 99.9% by mass or less. If the proportion of the lithium transition metal compound powder in the positive electrode active material layer is too large, the strength of the positive electrode tends to be insufficient, and if it is too small, the capacity may be insufficient.
The thickness of the positive electrode active material layer is usually about 10 to 200 μm.

The electrode density after pressing the positive electrode is usually 2.2 g / cm ³ or more and 4.2 g / cm ³ or less.
The positive electrode 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.
Thus, a positive electrode for a lithium secondary battery can be prepared.

[2. Negative electrode)
The negative electrode active material used for the negative electrode is described below. The negative electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. Specific examples include carbonaceous materials, alloy materials, lithium-containing metal composite oxide materials, and the like. These may be used individually by 1 type, and may be used together combining 2 or more types arbitrarily.

<Negative electrode active material>
Examples of the negative electrode active material include carbonaceous materials, alloy materials, lithium-containing metal composite oxide materials, and the like.
Examples of the carbonaceous material include (1) natural graphite, (2) artificial graphite, (3) amorphous carbon, (4) carbon-coated graphite, (5) graphite-coated graphite, and (6) resin-coated graphite. .

(1) Examples of natural graphite include scaly graphite, scaly graphite, soil graphite, and / or graphite particles obtained by subjecting these graphites to spheroidization or densification. Among these, spherical or ellipsoidal graphite subjected to spheroidizing treatment is particularly preferable from the viewpoints of particle filling properties and charge / discharge rate characteristics.
As an apparatus used for the spheroidization treatment, for example, an apparatus that repeatedly gives mechanical action such as compression, friction, shearing force, etc. including the interaction of particles mainly with impact force to the particles can be used. Specifically, it has a rotor with a large number of blades installed inside the casing, and mechanical action such as impact compression, friction, shearing force, etc. on the carbon material introduced inside the rotor by rotating at high speed. And a device for performing the spheroidizing treatment is preferable. Moreover, it is preferable to have a mechanism that repeatedly gives mechanical action by circulating the carbon material.

  For example, when the spheroidizing treatment is performed using the above-described apparatus, the peripheral speed of the rotating rotor is preferably 30 to 100 m / second, more preferably 40 to 100 m / second, and 50 to 100 m / second. More preferably. The treatment can be performed by simply passing a carbonaceous material, but it is preferable to circulate or stay in the apparatus for 30 seconds or longer, and it is preferable to circulate or stay in the apparatus for 1 minute or longer. More preferred.

  (2) Artificial graphite includes coal tar pitch, coal heavy oil, atmospheric residue, petroleum heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride, Organic compounds such as polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, imide resin are usually in the range of 2500 ° C. or higher and usually 3200 ° C. or lower. Examples thereof include those produced by graphitization at a temperature and, if necessary, pulverized and / or classified. At this time, a silicon-containing compound or a boron-containing compound can also be used as a graphitization catalyst. In addition, artificial graphite obtained by graphitizing mesocarbon microbeads separated in the heat treatment process of pitch can be mentioned. Furthermore, the artificial graphite of the granulated particle which consists of primary particles is also mentioned. For example, by mixing mesocarbon microbeads and graphitizable carbonaceous material powders such as coke, graphitizable binders such as tar and pitch, and graphitization catalyst, graphitizing, and pulverizing as necessary Examples of the resulting graphite particles include a plurality of flat particles and aggregated or bonded so that the orientation planes are non-parallel.

(3) As amorphous carbon, amorphous carbon that has been heat-treated at least once in a temperature range (400 to 2200 ° C.) in which no graphitizable carbon precursor such as tar or pitch is used as a raw material. Examples thereof include amorphous carbon particles that are heat-treated using particles or a non-graphitizable carbon precursor such as a resin as a raw material.
(4) Carbon-coated graphite can be obtained by mixing natural graphite and / or artificial graphite with a carbon precursor that is an organic compound such as tar, pitch, or resin, and heat-treating it at least once in the range of 400 to 2300 ° C. Examples thereof include a carbon graphite composite in which natural graphite and / or artificial graphite is used as nuclear graphite, and amorphous carbon coats the nuclear graphite. The composite form may cover the entire surface or a part thereof, or may be a composite of a plurality of primary particles using carbon originating from the carbon precursor as a binder. Carbon can also be deposited (CVD) by reacting natural graphite and / or artificial graphite with hydrocarbon gases such as benzene, toluene, methane, propane, and aromatic volatiles at a high temperature to deposit carbon on the graphite surface. A graphite composite can also be obtained.

(5) As graphite-coated graphite, natural graphite and / or artificial graphite and a carbon precursor of an easily graphitizable organic compound such as tar, pitch or resin are mixed and once in a range of about 2400 to 3200 ° C. Examples thereof include graphite-coated graphite in which natural graphite and / or artificial graphite obtained by heat treatment is used as nuclear graphite, and graphitized material covers the whole or part of the surface of nuclear graphite.
(6) As the resin-coated graphite, natural graphite and / or artificial graphite obtained by mixing natural graphite and / or artificial graphite with a resin and drying at a temperature of less than 400 ° C. is used as nuclear graphite, and the resin is nuclear graphite. And resin-coated graphite covering the surface.
Moreover, the carbonaceous material of (1)-(6) may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

Examples of organic compounds such as tar, pitch and resin used in the above (2) to (5) include coal-based heavy oil, direct-current heavy oil, cracked heavy oil, aromatic hydrocarbon, N-ring compound , S ring compound, polyphenylene, organic synthetic polymer, natural polymer, thermoplastic resin and carbonizable organic compound selected from the group consisting of thermosetting resins. The raw material organic compound may be used after being dissolved in a low molecular organic solvent in order to adjust the viscosity at the time of mixing.
Moreover, as natural graphite and / or artificial graphite used as a raw material of nuclear graphite, natural graphite subjected to spheroidization treatment is preferable.

  As an alloy material used as the negative electrode active material, as long as lithium can be occluded / released, lithium alone, simple metals and alloys forming lithium alloys, or oxides, carbides, nitrides, silicides, sulfides thereof Any of compounds such as products or phosphides may be used and is not particularly limited. The single metal and alloy forming the lithium alloy are preferably materials containing group 13 and group 14 metal / metalloid elements (that is, excluding carbon), more preferably aluminum, silicon and tin single metals and An alloy or compound containing these atoms. These may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

<Physical properties of carbonaceous materials>
When using a carbonaceous material as a negative electrode active material, it is desirable to have the following physical properties.
(X-ray parameters)
The d-value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction by the Gakushin method of carbonaceous materials is usually 0.335 nm or more, usually 0.360 nm or less, and 0.350 nm. The following is preferable, and 0.345 nm or less is more preferable. Further, the crystallite size (Lc) of the carbonaceous material obtained by X-ray diffraction by the Gakushin method is preferably 1.0 nm or more, and more preferably 1.5 nm or more.

(Volume-based average particle size)
The volume-based average particle diameter of the carbonaceous material is a volume-based average particle diameter (median diameter) obtained by a laser diffraction / scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and 7 μm. The above is particularly preferable, and is usually 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, and particularly preferably 25 μm or less.

If the volume-based average particle size is below the above range, the irreversible capacity may increase, leading to loss of initial battery capacity. On the other hand, when the above range is exceeded, when an electrode is produced by coating, an uneven coating surface tends to be formed, which may be undesirable in the battery production process.
The volume-based average particle size is measured by dispersing carbon powder in a 0.2% by weight aqueous solution (about 10 mL) of polyoxyethylene (20) sorbitan monolaurate, which is a surfactant, and laser diffraction / scattering particle size distribution. This is performed using a meter (for example, LA-700 manufactured by Horiba, Ltd.). The median diameter determined by the measurement is defined as the volume-based average particle diameter of the carbonaceous material of the present invention.

(Raman R value)
The Raman R value of the carbonaceous material is a value measured using a laser Raman spectrum method, and is usually 0.01 or more, preferably 0.03 or more, more preferably 0.1 or more, and usually 1. 5 or less, preferably 1.2 or less, more preferably 1 or less, and particularly preferably 0.5 or less.

When the Raman R value is below the above range, the crystallinity of the particle surface becomes too high, and there are cases where the number of sites where Li enters between layers decreases with charge / discharge. That is, charge acceptance may be reduced. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals are likely to be oriented in a direction parallel to the electrode plate, which may lead to a decrease in load characteristics.
On the other hand, if it exceeds the above range, the crystallinity of the particle surface is lowered, the reactivity with the non-aqueous electrolyte is increased, and the efficiency may be lowered and the gas generation may be increased.

The Raman spectrum is measured by using a Raman spectrometer (for example, a Raman spectrometer manufactured by JASCO Corporation) to drop the sample naturally into the measurement cell and filling the sample cell with argon ion laser light (or a semiconductor). While irradiating a laser beam, the cell is rotated in a plane perpendicular to the laser beam. The resulting Raman spectrum, the intensity _{I A} of the peak _{P A} in the vicinity of 1580 cm ^-1, and measuring the intensity _{I B} of a peak _{P B} in the vicinity of 1360 cm ^-1, the intensity ratio _{R (R = I B / I} A) Is calculated. The Raman R value calculated by the measurement is defined as the Raman R value of the carbonaceous material of the present invention.

Moreover, said Raman measurement conditions are as follows.
・ Laser wavelength: Ar ion laser 514.5 nm (semiconductor laser 532 nm)
Measurement range: 1100 cm ^{−1 to} 1730 cm ⁻¹
-Raman R value: background processing,
-Smoothing processing: Simple average, 5 points of convolution

(BET specific surface area)
BET specific surface area of the carbonaceous material is a value of the measured specific surface area using the BET method is usually 0.1 m ² · ^{g -1} or more, 0.7 m ² · ^{g -1} or more, 1. 0 m ² · ^{g -1} or more, and particularly preferably 1.5 m ² · ^{g -1} or more, generally not more than 100 m ² · ^{g -1,} preferably ^{25 m} 2 · ^{g -1} or less, 15 m ² · g ^-1 more preferably less, ^{10 m} 2 · ^{g -1} or less are especially preferred.

  When the value of the BET specific surface area is less than this range, the acceptability of lithium is likely to deteriorate during charging when used as a negative electrode material, lithium is likely to precipitate on the electrode surface, and stability may be reduced. On the other hand, if it exceeds this range, when used as a negative electrode material, the reactivity with the non-aqueous electrolyte increases, gas generation tends to increase, and a preferable battery may be difficult to obtain.

  The specific surface area is measured by the BET method using a surface area meter (for example, a fully automated surface area measuring device manufactured by Okura Riken), preliminarily drying the sample at 350 ° C. for 15 minutes under nitrogen flow, Using a nitrogen helium mixed gas that is accurately adjusted so that the relative pressure value of nitrogen is 0.3, the nitrogen adsorption BET one-point method is performed by a gas flow method.

(Roundness)
When the circularity is measured as the degree of the sphere of the carbonaceous material, it is preferably within the following range. The circularity is defined as “circularity = (peripheral length of an equivalent circle having the same area as the particle projection shape) / (actual perimeter of the particle projection shape)”, and is theoretical when the circularity is 1. Become a true sphere.
The degree of circularity of particles having a carbonaceous material particle size in the range of 3 to 40 μm is preferably closer to 1,
Moreover, 0.1 or more is preferable, 0.5 or more is preferable, 0.8 or more is more preferable, 0.85 or more is further more preferable, and 0.9 or more is especially preferable. High current density charge / discharge characteristics improve as the degree of circularity increases. Therefore, when the circularity is less than the above range, the filling property of the negative electrode active material is lowered, the resistance between particles is increased, and the high current density charge / discharge characteristics may be lowered for a short time.

  The circularity is measured using a flow type particle image analyzer (for example, FPIA manufactured by Sysmex Corporation). About 0.2 g of a sample was dispersed in a 0.2% by mass aqueous solution (about 50 mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant, and irradiated with 28 kHz ultrasonic waves at an output of 60 W for 1 minute. The detection range is specified as 0.6 to 400 μm, and the particle size is measured in the range of 3 to 40 μm.

  The method for improving the circularity is not particularly limited, but a sphere-shaped sphere is preferable because the shape of the interparticle void when the electrode body is formed is preferable. Examples of spheroidizing treatment include a method of mechanically approaching a sphere by applying a shearing force and a compressive force, a mechanical / physical processing method of granulating a plurality of fine particles by the binder or the adhesive force of the particles themselves, etc. Is mentioned.

(Tap density)
The tap density of the carbonaceous material is usually 0.1 g · cm ⁻³ or more, preferably 0.5 g · cm ⁻³ or more, more preferably 0.7 g · cm ⁻³ or more, and 1 g · cm ⁻³ or more. Particularly preferable, 2 g · cm ⁻³ or less is preferable, 1.8 g · cm ⁻³ or less is more preferable, and 1.6 g · cm ⁻³ or less is particularly preferable. When the tap density is below the above range, the packing density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, when the above range is exceeded, there are too few voids between particles in the electrode, it is difficult to ensure conductivity between the particles, and it may be difficult to obtain preferable battery characteristics.

The tap density is measured by passing through a sieve having an opening of 300 μm, dropping the sample onto a 20 cm ³ tapping cell and filling the sample to the upper end surface of the cell, and then measuring a powder density measuring instrument (for example, manufactured by Seishin Enterprise Co., Ltd. Using a tap denser, tapping with a stroke length of 10 mm is performed 1000 times, and the tap density is calculated from the volume at that time and the mass of the sample.

(Orientation ratio)
The orientation ratio of the carbonaceous material is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and usually 0.67 or less. When the orientation ratio is below the above range, the high-density charge / discharge characteristics may deteriorate. The upper limit of the above range is the theoretical upper limit value of the orientation ratio of the carbonaceous material.

The orientation ratio is measured by X-ray diffraction after pressure-molding the sample. Set the molded body obtained by filling 0.47 g of the sample into a molding machine with a diameter of 17 mm and compressing it with 58.8MN · m ^{-2 so} that it is flush with the surface of the sample holder for measurement. X-ray diffraction is measured. From the (110) diffraction and (004) diffraction peak intensities of the obtained carbon, a ratio represented by (110) diffraction peak intensity / (004) diffraction peak intensity is calculated.

The X-ray diffraction measurement conditions are as follows. “2θ” indicates a diffraction angle.
・ Target: Cu (Kα ray) graphite monochromator ・ Slit:
Divergence slit = 0.5 degree Light receiving slit = 0.15 mm
Scattering slit = 0.5 degree / measurement range and step angle / measurement time:
(110) plane: 75 degrees ≦ 2θ ≦ 80 degrees 1 degree / 60 seconds (004) plane: 52 degrees ≦ 2θ ≦ 57 degrees 1 degree / 60 seconds

(Aspect ratio (powder))
The aspect ratio of the carbonaceous material is usually 1 or more and usually 10 or less, preferably 8 or less, and more preferably 5 or less. If the aspect ratio exceeds the above range, streaking or a uniform coated surface cannot be obtained when forming an electrode plate, and the high current density charge / discharge characteristics may deteriorate. The lower limit of the above range is the theoretical lower limit value of the aspect ratio of the carbonaceous material.

  The aspect ratio is measured by magnifying and observing the carbonaceous material particles with a scanning electron microscope. Carbonaceous material particles when three-dimensional observation is performed by selecting arbitrary 50 graphite particles fixed to the end face of a metal having a thickness of 50 μm or less and rotating and tilting the stage on which the sample is fixed. The longest diameter A and the shortest diameter B orthogonal thereto are measured, and the average value of A / B is obtained.

<Configuration and production method of negative electrode>
Any known method can be used for producing the electrode as long as the effects of the present invention are not significantly impaired. For example, it is formed by adding a binder, a solvent, and, if necessary, a thickener, a conductive material, a filler, etc. to a negative electrode active material to form a slurry, which is applied to a current collector, dried and then pressed. Can do.
In the case of using an alloy-based material, a method of forming a thin film layer (negative electrode active material layer) containing the above-described negative electrode active material by a technique such as vapor deposition, sputtering, or plating is also used.

(Electrode density)
The electrode structure when the negative electrode active material is made into an electrode is not particularly limited, but the density of the negative electrode active material present on the current collector is preferably 1 g · cm ⁻³ or more, and 1.2 g · cm ⁻³ or more. but more preferably, particularly preferably 1.3 g · ^{cm -3} or more, preferably 2.2 g · ^{cm -3} or less, more preferably 2.1 g · ^{cm -3} or less, 2.0 g · ^{cm -3} or less Further preferred is 1.9 g · cm ⁻³ or less. When the density of the negative electrode active material existing on the current collector exceeds the above range, the negative electrode active material particles are destroyed, and the initial irreversible capacity increases or non-aqueous system near the current collector / negative electrode active material interface. There is a case where high current density charge / discharge characteristics are deteriorated due to a decrease in permeability of the electrolytic solution. On the other hand, if the amount is less than the above range, the conductivity between the negative electrode active materials decreases, the battery resistance increases, and the capacity per unit volume may decrease.

[3. (Separator)
Usually, a separator is interposed between the positive electrode and the negative electrode in order to prevent a short circuit. In this case, the nonaqueous electrolytic solution of the present invention is usually used by impregnating the separator.
The material and shape of the separator are not particularly limited, and known ones can be arbitrarily adopted as long as the effects of the present invention are not significantly impaired. Among them, a resin, glass fiber, inorganic material, etc. formed of a material that is stable with respect to the non-aqueous electrolyte solution of the present invention is used, and a porous sheet or a nonwoven fabric-like material having excellent liquid retention properties is used. Is preferred.

  As materials for the resin and glass fiber separator, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, glass filters and the like can be used. Of these, glass filters and polyolefins are preferred, and polyolefins are more preferred. These materials may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

The thickness of the separator is arbitrary, but is usually 1 μm or more, preferably 5 μm or more.
It is more preferably 0 μm or more, usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the separator is too thin than the above range, the insulating properties and mechanical strength may decrease. On the other hand, if it is thicker than the above range, not only the battery performance such as the rate characteristic may be lowered, but also the energy density of the whole non-aqueous electrolyte secondary battery may be lowered.

  Furthermore, when using a porous material such as a porous sheet or nonwoven fabric as the separator, the porosity of the separator is arbitrary, but is usually 20% or more, preferably 35% or more, more preferably 45% or more, Further, it is usually 90% or less, preferably 85% or less, and more preferably 75% or less. If the porosity is too smaller than the above range, the membrane resistance tends to increase and the rate characteristics tend to deteriorate. Moreover, when larger than the said range, it exists in the tendency for the mechanical strength of a separator to fall and for insulation to fall.

Moreover, although the average pore diameter of a separator is also arbitrary, it is 0.5 micrometer or less normally, 0.2 micrometer or less is preferable, and it is 0.05 micrometer or more normally. If the average pore diameter exceeds the above range, a short circuit tends to occur. On the other hand, below the above range, the film resistance may increase and the rate characteristics may deteriorate.
On the other hand, as inorganic materials, for example, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used. Used.

  As the form, a thin film shape such as a non-woven fabric, a woven fabric, or a microporous film is used. In the thin film shape, those having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferably used. In addition to the above-described independent thin film shape, a separator formed by forming a composite porous layer containing the inorganic particles on the surface layer of the positive electrode and / or the negative electrode using a resin binder can be used. For example, a porous layer may be formed by using alumina particles having a 90% particle size of less than 1 μm on both surfaces of the positive electrode and using a fluororesin as a binder.

  The characteristics of the separator in the non-electrolyte secondary battery can be grasped by the Gurley value. The Gurley value indicates the difficulty of air passage in the film thickness direction, and is expressed as the number of seconds required for 100 ml of air to pass through the film. It means that it is harder to go through. That is, a smaller value means better communication in the thickness direction of the film, and a larger value means lower communication in the thickness direction of the film. Communication is the degree of connection of holes in the film thickness direction. If the Gurley value of the separator of the present invention is low, it can be used for various purposes. For example, when used as a separator for a non-aqueous lithium secondary battery, a low Gurley value means that lithium ions can be easily transferred and is preferable because of excellent battery performance. Although the Gurley value of a separator is arbitrary, Preferably it is 10-1000 second / 100ml, More preferably, it is 15-800 second / 100ml, More preferably, it is 20-500 second / 100ml. If the Gurley value is 1000 seconds / 100 ml or less, the electrical resistance is substantially low, which is preferable as a separator.

[Battery design]
<Electrode group>
The electrode group has a laminated structure in which the positive electrode plate and the negative electrode plate are interposed through the separator, and a structure in which the positive electrode plate and the negative electrode plate are wound in a spiral shape through the separator. Either is acceptable. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupation ratio) is usually 40% or more, preferably 50% or more, and usually 90% or less, preferably 80% or less. .

  When the electrode group occupancy is below the above range, the battery capacity decreases. Also, if the above range is exceeded, the void space is small, the battery expands, and the member expands or the vapor pressure of the electrolyte liquid component increases and the internal pressure rises. In some cases, the gas release valve that lowers various characteristics such as storage at high temperature and the like, or releases the internal pressure to the outside is activated.

<Exterior case>
The material of the outer case is not particularly limited as long as it is a substance that is stable with respect to the non-aqueous electrolyte used. Specifically, a nickel-plated steel plate, stainless steel, aluminum, an aluminum alloy, a metal such as a magnesium alloy, or a laminated film (laminate film) of a resin and an aluminum foil is used. From the viewpoint of weight reduction, an aluminum or aluminum alloy metal or a laminate film is preferably used.

  In an exterior case using metals, the metal is welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed sealed structure, or a caulking structure using the above metals via a resin gasket. Things. Examples of the outer case using the laminate film include a case where a resin-sealed structure is formed by heat-sealing resin layers. In order to improve sealing performance, a resin different from the resin used for the laminate film may be interposed between the resin layers. In particular, when a resin layer is heat-sealed through a current collecting terminal to form a sealed structure, a metal and a resin are joined, so that a resin having a polar group or a modified group having a polar group introduced as an intervening resin is used. Resins are preferably used.

<Protective element>
Protection elements such as PTC (Positive Temperature Coefficient), thermal fuse, thermistor, whose resistance increases when abnormal heat is generated or excessive current flows, cut off the current flowing through the circuit due to sudden increase in battery internal pressure or internal temperature during abnormal heat generation A valve (current cutoff valve) or the like can be used. It is preferable to select a protective element that does not operate under normal use at a high current, and it is more preferable that the protective element is designed so as not to cause abnormal heat generation or thermal runaway even without the protective element.

<Exterior body>
The non-aqueous electrolyte secondary battery of the present invention is usually configured by housing the non-aqueous electrolyte, the negative electrode, the positive electrode, the separator, and the like in an exterior body. This exterior body is not particularly limited, and any known one can be arbitrarily adopted as long as the effects of the present invention are not significantly impaired. Specifically, the material of the exterior body is arbitrary, but usually, for example, nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, or the like is used.
The shape of the exterior body is also arbitrary, and may be any of a cylindrical shape, a square shape, a laminate shape, a coin shape, a large size, and the like.

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 mass 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 mass of polyvinylidene fluoride (hereinafter referred to as “PVdF” as appropriate) and acetylene black 3 parts by mass was mixed, and a slurry obtained by adding N-methylpyrrolidone 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 mass of graphite powder, which is a negative electrode active material, and 6 parts by mass of PVdF, adding N-methylpyrrolidone into a slurry, and applying 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 solution 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 to 4.1 V with a current corresponding to 0.2 C (hereinafter referred to as “CCCV charging” as appropriate) 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 4.2V at 0.2C, it discharged again to 3V at 0.5C, and the initial discharge capacity was calculated | required. 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.

[Storage characteristics evaluation test]
After the capacity evaluation, the battery was charged to 4.2 V at 0.2 C in a constant temperature bath at 25 ° C., and then stored in a high temperature bath at 75 ° C. for 3 days. Thereafter, the battery was cooled to 25 ° C. and immediately immersed in an ethanol bath to measure the buoyancy (Archimedes principle) to determine the amount of gas generated. Subsequently, the battery was again charged CCCV to 4.2 V at 0.2 C, and then discharged to 3 V at 0.5 C, and the capacity after storage was determined. The capacity recovery rate was calculated from the discharge capacity before and after storage by the following formula.

Capacity recovery rate (%) = discharge capacity after storage (mAh / g) / initial discharge capacity (mAh / g)
< Reference Example 1>
LiPF ₆ , ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propionate and hexamethylene diisocyanate are mixed so as to have a mass ratio of 15.5 / 21/17/16/30 / 0.5, and a nonaqueous electrolytic solution It was. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was prepared according to the above-described method, and a capacity evaluation test and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 1 >
A secondary battery was prepared and evaluated in the same manner as in Reference Example 1 except that 1,3-bis (isocyanatomethyl) cyclohexane was used instead of hexamethylene diisocyanate. The results are shown in Table 1.
<Example 2 >
A secondary battery was prepared and evaluated in the same manner as in Reference Example 1 except that tetramethylene diisocyanate was used instead of hexamethylene diisocyanate. The results are shown in Table 1.

<Example 3 >
A secondary battery was prepared and evaluated in the same manner as in Reference Example 1 except that dicyclohexylmethane-4,4′-diisocyanate was used instead of hexamethylene diisocyanate. The results are shown in Table 1.
<Example 4 >
Reference Example 1 except that Duranate ^TM TPA-100 [manufactured by Asahi Kasei Chemicals Co., Ltd., general formula (4), Z ₁ = — (CH ₂ ) ₆ —] was used instead of hexamethylene diisocyanate.
A secondary battery was prepared and evaluated in the same manner as described above. The results are shown in Table 1.

<Example 5 >
LiPF ₆ , ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propionate and 1,3-bis (isocyanatomethyl) cyclohexane so that the mass ratio is 15.5 / 21/17/15/30 / 1.5 To make a non-aqueous electrolyte. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was prepared according to the above-described method, and a capacity evaluation test and a storage characteristic evaluation test were performed. The results are shown in Table 1.

< Reference Example 2 >
LiPF ₆ , ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propionate and hexamethylene diisocyanate are mixed so that the mass ratio is 17.5 / 32/34/8/8 / 0.5, and a non-aqueous electrolyte solution It was. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was prepared according to the above-described method, and a capacity evaluation test and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Reference Example 3>
LiPF ₆ , ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethyl acetate and hexamethylene diisocyanate are mixed so as to have a mass ratio of 17.5 / 32/34/8/8 / 0.5, and a non-aqueous electrolyte solution did. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was prepared according to the above-described method, and a capacity evaluation test and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Reference Example 4>
LiPF ₆ , ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, vinylene carbonate, methyl propionate and hexamethylene diisocyanate are mixed so that the mass ratio is 15.5 / 21/17/15/1/30 / 0.5. Thus, a non-aqueous electrolyte solution was obtained. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was prepared according to the above-described method, and a capacity evaluation test and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Comparative Example 1>
Without using hexamethylene diisocyanate, LiPF ₆ , ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate and methyl propionate are mixed so as to have a mass ratio of 15.5 / 21/17 / 16.5 / 30 and are non-aqueous An electrolyte was used. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was prepared according to the above-described method, and a capacity evaluation test and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Comparative example 2>
LiPF ₆ , ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propionate and hexamethylene diisocyanate are mixed so as to have a mass ratio of 15.5 / 21/44/16/3 / 0.5, and a non-aqueous electrolyte solution It was. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was prepared according to the above-described method, and a capacity evaluation test and a storage characteristic evaluation test were performed. 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 phenyl isocyanate was used instead of hexamethylene diisocyanate. The results are shown in Table 1. In Table 1, MP represents methyl propionate, EA represents ethyl acetate, EC represents ethylene carbonate, DMC represents dimethyl carbonate, EMC represents ethyl methyl carbonate, and VC represents vinylene carbonate.

From Table 1, when using the non-aqueous electrolytes of Examples 1 to 5 and Reference Examples 1 to 4 according to the present invention,
It can be seen that gas generation after the storage test is greatly suppressed, and that a high capacity recovery rate can be achieved after the storage test. That is, in the case where the isocyanate compound of the present invention is not contained (Comparative Example 1), although the capacity recovery rate is high, gas generation is large. On the other hand, even when the isocyanate compound of the present invention is contained, when the content of the chain carboxylic acid ester deviates from a predetermined amount (Comparative Example 2), gas generation is suppressed, but the capacity recovery rate is greatly reduced. Resulting in. When the isocyanate compound of the present invention and a predetermined amount of a chain carboxylic acid ester are contained, a synergistic effect is exhibited, and both gas generation suppression and a high capacity recovery rate are achieved. Even if an isocyanate which is not an isocyanate compound of the present invention is contained, no particular effect is exhibited (Comparative Example 3).

  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 (6)

A non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous organic solvent, the non-aqueous electrolyte solution containing a chain carboxylic acid ester in an amount of 5 to 70% by mass with respect to the mass of the non-aqueous electrolyte solution, and unsaturated A cyclic carbonate is contained in an amount of 0.3% by mass or more and 2% by mass or less with respect to the mass of the non-aqueous electrolyte, and further a compound having two or more isocyanate groups is 0.1% by mass or more with respect to the mass of the non-aqueous electrolyte. A non-aqueous electrolyte solution containing 2% by mass or less (except when the non-aqueous electrolyte solution contains hexamethylene diisocyanate). The non-aqueous electrolyte solution according to claim 1 , wherein the chain carboxylic acid ester is a chain carboxylic acid ester represented by the following general formula (1).
R ₁ COOR ₂ (1)
(Wherein R ₁ and R ₂ are each independently a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with fluorine) The nonaqueous electrolytic solution further contains at least one selected from monofluorophosphate and difluorophosphate in an amount of 0.001 to 10% by mass based on the mass of the nonaqueous electrolytic solution. The non-aqueous electrolyte solution according to 1 or 2 . The non-aqueous electrolysis according to any one of claims 1 to 3 , wherein the non-aqueous electrolyte further contains 0.001 to 30% by mass of a fluorine-substituted cyclic carbonate with respect to the mass of the non-aqueous electrolyte. liquid. The compound having two or more isocyanate groups is selected from 1,3-bis (isocyanatomethyl) cyclohexane, tetramethylene diisocyanate, dicyclohexylmethane-4,4′-diisocyanate and a compound represented by the following general formula (4). The non-aqueous electrolyte solution according to any one of claims 1 to 4 , wherein

(In the formula, Z ₁ is a hydrocarbon group having 1 to 16 carbon atoms which may be substituted with fluorine) A lithium secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to any one of claims 1 to 5. Rechargeable lithium battery.

(that's all)