JP5699465B2 - 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 nonaqueous solvent as main components. The non-aqueous 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 have been evaluated for various characteristics such as initial capacity, rate characteristics, cycle characteristics, high temperature storage characteristics, low temperature characteristics, continuous charge characteristics, self-discharge characteristics, overcharge prevention characteristics, etc. For this purpose, many methods have been reported so far in which various auxiliary agents are contained in the electrolyte solution in small amounts. For example, it has been proposed to contain a fluorine-substituted aromatic compound as an auxiliary agent. Patent Document 1 discloses a non-aqueous electrolyte secondary battery using an electrolytic solution containing a phosphate ester compound and an ether or ester compound having a halogen-substituted phenyl group. Specifically, self-discharge characteristics during storage at 45 ° C. are improved by using an electrolytic solution containing trimethyl phosphate (TMP) and 3-fluoroanisole. Patent Document 2 describes that aromatic compounds such as 1-acetoxy-2-fluorobenzene, 1-acetoxy-3-fluorobenzene, and 1-acetoxy-4-fluorobenzene are effective as an additive for batteries. However, it has not been clarified as to what specific characteristics should be improved.

JP 2003-282055 A Special table 2009-512418 gazette

  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. Above all, improvement of safety such as overcharge characteristics is urgent. However, when an additive is added to the electrolytic solution in order to improve the overcharge characteristics, the storage characteristics are often deteriorated. Although it describes later as a comparative example, when the electrolyte solution currently disclosed by patent document 1 was used, the remarkable deterioration of a storage characteristic was seen.

  The present invention has been made in view of the above problems, and an object thereof is to provide an electrolytic solution and a lithium secondary battery having improved overcharge characteristics and improved storage characteristics.

As a result of intensive studies to solve the above problems, the inventor of the present invention has obtained 90% by volume in total of those selected from the group consisting of saturated cyclic carbonates, chain carbonates and aliphatic carboxylic acid esters. Overcharge characteristics are improved by using a non-aqueous electrolyte characterized by containing a specific amount of the fluorine-substituted aromatic ester compound in a specific amount with respect to the weight of the non-aqueous electrolyte. And it discovered that a preservation | save characteristic was improved and completed this invention.

That is, the gist of the present invention is as follows.
[1] In a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous organic solvent, the non-aqueous organic solvent is at least one selected from the group consisting of saturated cyclic carbonates, chain carbonates, and aliphatic carboxylic acid esters. The total amount of the fluorine-substituted aromatic ester compound represented by the following general formula (1) is 0.01 to 10% by weight with respect to the total weight of the non-aqueous electrolyte. A non-aqueous electrolyte characterized by that.

(In the formula, R ₁ is a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a fluorine atom,
X is a fluorine atom or a C1-C12 fluorine-substituted alkyl group, and n is an integer of 1-4.
[2] The saturated cyclic carbonate contains at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, monofluoroethylene carbonate, and difluoroethylene carbonate. Non-aqueous electrolyte.
[3] The above [1] or [3], wherein the chain carbonate contains at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate. 2].
[4] The non-setting according to [1] to [3], wherein the aliphatic carboxylic acid ester contains at least one selected from the group of compounds represented by the following general formula (2): Aqueous electrolyte.

(In the formula, R ₂ and R ₃ each represent an alkyl group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and each may be the same or different.)
[5] The non-aqueous electrolyte further comprises at least one selected from the group consisting of unsaturated cyclic carbonates, monofluorophosphates, difluorophosphates, sultone, and sulfites, based on the total weight of the non-aqueous electrolyte. The non-aqueous electrolyte solution according to any one of the above [1] to [4], which is contained in an amount of 0.01 to 10% by weight.
[6] A non-aqueous electrolyte battery including a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution is any one of [1] to [5]. A lithium secondary battery, which is a non-aqueous electrolyte.

  According to the present invention, when used in a lithium secondary battery, the overcharge characteristics can be greatly improved and the storage characteristics can be improved, and an excellent lithium secondary battery using the electrolyte 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 lithium secondary battery of the present invention includes a non-aqueous electrolyte, a positive electrode, and a negative electrode. 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 solution in which a lithium salt is dissolved in a non-aqueous organic solvent, and the non-aqueous organic solvent is saturated. Fluorine-substituted fragrance containing at least one selected from the group consisting of cyclic carbonates, chain carbonates and aliphatic carboxylic acid esters in a total ratio exceeding 90% by volume, and further represented by the following general formula (1) A non-aqueous electrolyte solution containing 0.01 to 10% by weight of a group ester compound (hereinafter referred to as “the fluorine-substituted aromatic ester compound in the present invention” as appropriate) based on the weight of the non-aqueous electrolyte solution.

(In the formula, R ₁ is a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a fluorine atom,
X is a fluorine atom or a C1-C12 fluorine-substituted alkyl group, and n is an integer of 1-4.
[1. Fluorine-substituted aromatic ester compound]
[1-1. type]
The non-aqueous electrolyte solution in the present invention contains a fluorine-substituted aromatic ester compound represented by the following general formula (1).

(In the formula, R ₁ is a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a fluorine atom,
X is a fluorine atom or a C1-C12 fluorine-substituted alkyl group, and n is an integer of 1-4.
In the general formula (1), R ₁ is a hydrocarbon group and may be substituted with fluorine. Examples of preferred hydrocarbon groups as R ₁ include alkyl groups, aryl groups, alkenyl groups, aralkyl groups, and the like. Of these, an alkyl group and an aryl group are preferable, and an alkyl group is more preferable.

When R ₁ is an alkyl group, the alkyl group usually has 1 to 12, preferably 1 to 8, more preferably 1 to 4, more preferably 1 to 2, and most preferably 1. If the number of carbon atoms is too large, the solubility of the fluorine-substituted aromatic ester compound in the non-aqueous electrolyte solution is deteriorated, and the effect may not be sufficiently exhibited. Specific examples of preferred alkyl groups for R include methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl and the like. Among these, a methyl group, an ethyl group, a propyl group, and a butyl group are more preferable, a methyl group and an ethyl group are more preferable, and a methyl group is most preferable.

When R ₁ is an alkenyl group, the carbon number of the alkenyl group is usually 2 to 12, preferably 2 to 8, more preferably 2 to 4, more preferably 2 to 3, and most preferably 2. If the number of carbon atoms is too large, the solubility of the fluorine-substituted aromatic ester compound in the non-aqueous electrolyte solution is deteriorated, and the effect may not be sufficiently exhibited. Specific examples of preferred alkenyl groups for R include vinyl, isopropenyl, and allyl groups. Among these, a vinyl group is more preferable.

When R ₁ is an aryl group, the aryl group usually has 6 to 12 carbon atoms. Specific examples include phenyl group, tolyl group, ethylphenyl group, dimethylphenyl group, isopropyl group, t-butylphenyl group, t-amylphenyl group, cyclohexylphenyl group, α-naphthyl group, β-naphthyl group and the like. . Among these, a phenyl group, a t-butylphenyl group, and a t-amylphenyl group are more preferable.

When R ₁ is an aralkyl group, the aralkyl group usually has 7 to 12 carbon atoms. Specific examples include benzyl group, α-phenethyl group, β-phenethyl group and the like. Among these, a benzyl group is more preferable.
As for R ₁ , some or all of the hydrogen atoms constituting the hydrocarbon group may be substituted with fluorine atoms. Specific examples include a monofluoromethyl group, a difluoromethyl group, a trimethylfluoromethyl group, a 2,2,2-trifluoroethyl group, a pentafluoroethyl group, a monofluorophenyl group, and a pentafluorophenyl group.

In the general formula (1), X is a fluorine atom or a fluorine-substituted alkyl group having 1 to 12 carbon atoms, preferably a fluorine atom.
When X is a fluorine-substituted alkyl group, the alkyl group usually has 1 to 12, preferably 1 to 8, more preferably 1 to 4, still more preferably 1 to 2, and most preferably 1. Specific examples of the preferred fluorine-substituted alkyl group as X include a monofluoromethyl group,
Examples include a difluoromethyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group, a pentafluoroethyl group, a perfluorobutyl group, a perfluorooctyl group, and a perfluorododecyl group. Among these, a monofluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group, and a pentafluoroethyl group are preferable, and a monofluoromethyl group, a difluoromethyl group, and a trifluoromethyl group are more preferable. Preferred is a trifluoromethyl group.

Moreover, in the said General formula (1), n is an integer of 1-4, Preferably it is 1-3, More preferably, it is 1. When n number becomes large, it becomes expensive and difficult to obtain, and tends to be difficult to use in a lithium secondary battery.
The molecular weight of the fluorine-substituted aromatic ester compound in the present invention is usually 150 or more, and usually 400 or less, preferably 250 or less. If the upper limit of this range is exceeded, the solubility in the non-aqueous electrolyte in the present invention may be lowered, and the effects of the present invention may not be sufficiently exhibited.

Specific examples of the fluorine-substituted aromatic ester compound in the present invention are as follows:
2-fluorophenyl acetate,
3-fluorophenyl acetate,
4-fluorophenyl acetate,
2,3-difluorophenyl acetate,
2,4-difluorophenyl acetate,
2,5-difluorophenyl acetate,
2,6-difluorophenyl acetate,
3,4-difluorophenyl acetate,
3,5-difluorophenyl acetate,
2,3,4-trifluorophenyl acetate,
2,3,5-trifluorophenyl acetate,
2,3,6-trifluorophenyl acetate,
2,4,5-trifluorophenyl acetate,
2,4,6-trifluorophenyl acetate,
3,4,5-trifluorophenyl acetate,
2,3,4,5-tetrafluorophenyl acetate,
Fluorine-substituted phenyl acetates such as
2-trifluoromethylphenyl acetate,
3-trifluoromethylphenyl acetate,
4-trifluoromethylphenyl acetate,
2,3-bis (trifluoromethyl) phenyl acetate,
2,4-bis (trifluoromethyl) phenyl acetate,
2,5-bis (trifluoromethyl) phenyl acetate,
2,6-bis (trifluoromethyl) phenyl acetate,
3,4-bis (trifluoromethyl) phenyl acetate,
3,5-bis (trifluoromethyl) phenyl acetate,
Fluorine-substituted alkylphenyl acetates such as
2-fluorophenylpropionate,
3-fluorophenylpropionate,
4-fluorophenylpropionate,
2,3-difluorophenylpropionate,
2,4-difluorophenylpropionate,
2,5-difluorophenylpropionate,
2,6-difluorophenylpropionate,
3,4-difluorophenylpropionate,
3,5-difluorophenylpropionate,
2,3,4-trifluorophenylpropionate,
2,3,5-trifluorophenylpropionate,
2,3,6-trifluorophenylpropionate,
2,4,5-trifluorophenylpropionate,
2,4,6-trifluorophenylpropionate,
3,4,5-trifluorophenylpropionate,
2,3,4,5-tetrafluorophenylpropionate,
Fluorine-substituted phenylpropionates such as
2-trifluoromethylphenylpropionate,
3-trifluoromethylphenylpropionate,
4-trifluoromethylphenylpropionate,
2,3-bis (trifluoromethyl) phenylpropionate,
2,4-bis (trifluoromethyl) phenylpropionate,
2,5-bis (trifluoromethyl) phenylpropionate,
2,6-bis (trifluoromethyl) phenylpropionate,
3,4-bis (trifluoromethyl) phenylpropionate,
3,5-bis (trifluoromethyl) phenylpropionate,
Fluorine-substituted alkylphenylpropionates such as;
2-fluorophenyl butyrate,
3-fluorophenyl butyrate,
4-fluorophenyl butyrate,
2,3-difluorophenyl butyrate,
2,4-difluorophenyl butyrate,
2,5-difluorophenyl butyrate,
2,6-difluorophenyl butyrate,
3,4-difluorophenyl butyrate,
3,5-difluorophenyl butyrate,
2,3,4-trifluorophenyl butyrate,
2,3,5-trifluorophenyl butyrate,
2,3,6-trifluorophenyl butyrate,
2,4,5-trifluorophenyl butyrate,
2,4,6-trifluorophenylbutyrate,
3,4,5-trifluorophenyl butyrate,
2,3,4,5-tetrafluorophenyl butyrate,
Fluorine-substituted phenylbutyrates such as
2-fluorophenyl butyrate,
3-fluorophenyl butyrate,
4-fluorophenyl butyrate,
2,3-difluorophenyl butyrate,
2,4-difluorophenyl butyrate,
2,5-difluorophenyl butyrate,
2,6-difluorophenyl butyrate,
3,4-difluorophenyl butyrate,
3,5-difluorophenyl butyrate,
2,3,4-trifluorophenyl butyrate,
2,3,5-trifluorophenyl butyrate,
2,3,6-trifluorophenyl butyrate,
2,4,5-trifluorophenyl butyrate,
2,4,6-trifluorophenylbutyrate,
3,4,5-trifluorophenyl butyrate,
2,3,4,5-tetrafluorophenyl butyrate,
Fluorine-substituted phenylbutyrates such as
2-fluorophenylbenzoate,
3-fluorophenylbenzoate,
4-fluorophenylbenzoate,
2,3-difluorophenylbenzoate,
2,4-difluorophenylbenzoate,
2,5-difluorophenylbenzoate,
2,6-difluorophenylbenzoate,
3,4-difluorophenylbenzoate,
3,5-difluorophenylbenzoate,
2,3,4-trifluorophenylbenzoate,
2,3,5-trifluorophenylbenzoate,
2,3,6-trifluorophenylbenzoate,
2,4,5-trifluorophenylbenzoate,
2,4,6-trifluorophenylbenzoate,
3,4,5-trifluorophenylbenzoate,
2,3,4,5-tetrafluorophenylbenzoate,
Fluorine-substituted phenylbenzoates such as
2-fluorophenyl acrylate,
3-fluorophenyl acrylate,
4-fluorophenyl acrylate,
2,3-difluorophenyl acrylate,
2,4-difluorophenyl acrylate,
2,5-difluorophenyl acrylate,
2,6-difluorophenyl acrylate,
3,4-difluorophenyl acrylate,
3,5-difluorophenyl acrylate,
2,3,4-trifluorophenyl acrylate,
2,3,5-trifluorophenyl acrylate,
2,3,6-trifluorophenyl acrylate,
2,4,5-trifluorophenyl acrylate,
2,4,6-trifluorophenyl acrylate,
3,4,5-trifluorophenyl acrylate,
2,3,4,5-tetrafluorophenyl acrylate,
Fluorine-substituted phenyl acrylates such as
2-fluorophenyl difluoroacetate,
3-fluorophenyl difluoroacetate,
4-fluorophenyl difluoroacetate,
2,3-difluorophenyl difluoroacetate,
2,4-difluorophenyl difluoroacetate,
2,5-difluorophenyl difluoroacetate,
2,6-difluorophenyl difluoroacetate,
3,4-difluorophenyl difluoroacetate,
3,5-difluorophenyl difluoroacetate,
2,3,4-trifluorophenyl difluoroacetate,
2,3,5-trifluorophenyl difluoroacetate,
2,3,6-trifluorophenyl difluoroacetate,
2,4,5-trifluorophenyl difluoroacetate,
2,4,6-trifluorophenyl difluoroacetate,
3,4,5-trifluorophenyl difluoroacetate,
2,3,4,5-tetrafluorophenyl difluoroacetate,
Fluorine-substituted phenyl difluoroacetates such as
2-fluorophenyl trifluoroacetate,
3-fluorophenyl trifluoroacetate,
4-fluorophenyl trifluoroacetate,
2,3-difluorophenyl trifluoroacetate,
2,4-difluorophenyl trifluoroacetate,
2,5-difluorophenyl trifluoroacetate,
2,6-difluorophenyl trifluoroacetate,
3,4-difluorophenyl trifluoroacetate,
3,5-difluorophenyl trifluoroacetate,
2,3,4-trifluorophenyl trifluoroacetate,
2,3,5-trifluorophenyl trifluoroacetate,
2,3,6-trifluorophenyl trifluoroacetate,
2,4,5-trifluorophenyl trifluoroacetate,
2,4,6-trifluorophenyl trifluoroacetate,
3,4,5-trifluorophenyl trifluoroacetate,
2,3,4,5-tetrafluorophenyl trifluoroacetate,
Fluorine-substituted phenyl trifluoroacetates such as;
2-fluorophenyl pentafluoropropionate,
3-fluorophenyl pentafluoropropionate,
4-fluorophenyl pentafluoropropionate,
2,3-difluorophenyl pentafluoropropionate,
2,4-difluorophenyl pentafluoropropionate,
2,5-difluorophenyl pentafluoropropionate,
2,6-difluorophenyl pentafluoropropionate,
3,4-difluorophenyl pentafluoropropionate,
3,5-difluorophenyl pentafluoropropionate,
2,3,4-trifluorophenyl pentafluoropropionate,
2,3,5-trifluorophenyl pentafluoropropionate,
2,3,6-trifluorophenyl pentafluoropropionate,
2,4,5-trifluorophenyl pentafluoropropionate,
2,4,6-trifluorophenyl pentafluoropropionate,
3,4,5-trifluorophenyl pentafluoropropionate,
2,3,4,5-tetrafluorophenyl pentafluoropropionate,
Fluorine-substituted phenylpentafluoropropionates such as;
Etc.
Among them, 2-fluorophenyl acetate,
3-fluorophenyl acetate,
4-fluorophenyl acetate,
2,4-difluorophenyl acetate,
2,5-difluorophenyl acetate,
2,6-difluorophenyl acetate,
3,4-difluorophenyl acetate,
3,5-difluorophenyl acetate,
2,3,4-trifluorophenyl acetate,
2,3,5-trifluorophenyl acetate,
2,3,6-trifluorophenyl acetate,
2,4,6-trifluorophenyl acetate,
2,3,4,5-tetrafluorophenyl acetate,
Fluorine-substituted phenyl acetates such as
2-trifluoromethylphenyl acetate,
3-trifluoromethylphenyl acetate,
Fluorine-substituted alkylphenyl acetates such as 4-trifluoromethylphenyl acetate;
2-fluorophenylpropionate,
3-fluorophenylpropionate,
4-fluorophenylpropionate,
2,4-difluorophenylpropionate,
2,5-difluorophenylpropionate,
2,6-difluorophenylpropionate,
3,4-difluorophenylpropionate,
3,5-difluorophenylpropionate,
2,3,4-trifluorophenylpropionate,
2,3,5-trifluorophenylpropionate,
2,3,6-trifluorophenylpropionate,
2,4,6-trifluorophenylpropionate,
2,3,4,5-tetrafluorophenylpropionate,
Fluorine-substituted phenylpropionates such as
2-fluorophenyl trifluoroacetate,
3-fluorophenyl trifluoroacetate,
4-fluorophenyl trifluoroacetate,
2,3-difluorophenyl trifluoroacetate,
2,4-difluorophenyl trifluoroacetate,
2,5-difluorophenyl trifluoroacetate,
2,6-difluorophenyl trifluoroacetate,
3,4-difluorophenyl trifluoroacetate,
3,5-difluorophenyl trifluoroacetate,
2,3,4-trifluorophenyl trifluoroacetate,
2,3,5-trifluorophenyl trifluoroacetate,
2,3,6-trifluorophenyl trifluoroacetate,
2,4,5-trifluorophenyl trifluoroacetate,
2,4,6-trifluorophenyl trifluoroacetate,
3,4,5-trifluorophenyl trifluoroacetate,
2,3,4,5-tetrafluorophenyl trifluoroacetate,
Fluorine-substituted phenyl trifluoroacetates such as;
Is preferred.

Among these, 2-fluorophenyl acetate,
3-fluorophenyl acetate,
4-fluorophenyl acetate,
2,4-difluorophenyl acetate,
2,5-difluorophenyl acetate,
2,6-difluorophenyl acetate,
3,4-difluorophenyl acetate,
3,5-difluorophenyl acetate,
2,3,4-trifluorophenyl acetate,
2,3,5-trifluorophenyl acetate,
2,3,6-trifluorophenyl acetate,
2,4,6-trifluorophenyl acetate,
2,3,4,5-tetrafluorophenyl acetate,
More preferred are fluorine-substituted phenyl acetates such as 2-fluorophenyl acetate,
3-fluorophenyl acetate,
4-fluorophenyl acetate,
2,4-difluorophenyl acetate,
3,4-difluorophenyl acetate,
2,3,4-trifluorophenyl acetate,
Particularly preferred are fluorine-substituted phenyl acetates.
Moreover, the fluorine substituted aromatic ester compound in this invention mentioned above may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

[1-2. composition]
The addition amount of the fluorine-substituted aromatic ester compound in the present invention is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 0.3% by weight with respect to the total weight of the non-aqueous electrolyte. % Or more, usually 10% by weight or less, preferably 7% by weight or less, more preferably 5% by weight or less, and still more preferably 4% by weight or less. If the amount added is too large, the high-temperature storage characteristics tend to deteriorate, and further, the amount of gas generated during normal battery use increases, and the capacity retention rate may decrease. On the other hand, if the concentration is too small, the effects of the present invention may not be sufficiently exhibited. The fluorine-substituted aromatic ester compound is not included in the total of the non-aqueous organic solvents defined in claim 1.

[2. Non-aqueous organic solvent]
[2-1. Saturated cyclic carbonate]
The saturated cyclic carbonate according to the present invention can be arbitrarily selected as long as it is a cyclic carbonate having no carbon-carbon unsaturated bond and does not significantly impair the effects of the present invention. For example, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl ethylene carbonate, diethyl ethylene carbonate, monopropyl ethylene carbonate, dipropyl ethylene carbonate, phenyl ethylene carbonate, diphenyl ethylene carbonate, catechol carbonate; monofluoro ethylene carbonate, difluoro Ethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, monofluoromethyl ethylene carbonate, trifluoromethyl ethylene carbonate, monochloroethylene carbonate, dichloroethylene carbonate, trichloroethylene carbonate, tetrachloroethylene carbonate, monochloromethyl Ethylene carbonate, halogen substituted carbonates such as trichloromethyl ethylene carbonate.

  Among these, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, monofluoroethylene carbonate, and difluoroethylene carbonate is preferable. Furthermore, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, and monofluoroethylene carbonate is particularly preferable in order to improve storage characteristics.

[2-2. Chain carbonate]
The chain carbonate according to the present invention can be arbitrarily selected as long as the effects of the present invention are not significantly impaired. For example, 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, methyl trifluoromethyl carbonate, bis Examples include halogen-substituted carbonates such as (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 at least one of dimethyl carbonate and ethyl methyl carbonate. It is particularly preferred.
[2-3. Aliphatic carboxylic acid ester]
The aliphatic carboxylic acid ester according to the present invention can be arbitrarily selected as long as the effects of the present invention are not significantly impaired. Among them, the aliphatic carboxylic acid ester contains at least one selected from the group of compounds represented by the following general formula (2). It is preferable to do.

(In the formula, R ₂ and R ₃ each represent an alkyl group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and each may be the same or different.)
In the above general formula (2), R ₂ is an alkyl group and may be substituted with fluorine. The carbon number of R ₂ is usually 1 to 4, preferably 1 to 3, more preferably 1 to 2, and most preferably 2. If the number of carbon atoms is too large, the viscosity of the non-aqueous electrolyte increases, which may hinder the movement of lithium ions and deteriorate the performance. Preferable examples when R ₂ is an alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group. Among these, a methyl group, an ethyl group, and a propyl group are more preferable, a methyl group and an ethyl group are more preferable, and an ethyl group is most preferable. Preferred examples when R ₂ is a fluorine-substituted alkyl group include monofluoromethyl group, difluoromethyl group, trimethylfluoromethyl group, 2,2,2-trifluoroethyl group, pentafluoroethyl group, hepta Examples include a fluoropropyl group. Among these, monofluoromethyl group, difluoromethyl group, trimethylfluoromethyl group, 2,2,2-trifluoroethyl group, pentafluoroethyl group are preferable, 2,2,2-trifluoroethyl group, pentafluoroethyl group Is most preferred.

In the general formula (2), R ₃ is an alkyl group, which may be substituted with fluorine. The carbon number of R ₃ is usually 1 to 4, preferably 1 to 3, and more preferably 1 to 2. If the number of carbon atoms is too large, the viscosity of the non-aqueous electrolyte increases, which may hinder the movement of lithium ions and deteriorate the performance. Preferable examples when R ₃ is an alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group. Among these, a methyl group, an ethyl group, and a propyl group are more preferable, and a methyl group and an ethyl group are more preferable. Preferred examples when R ₃ is a fluorine-substituted alkyl group include monofluoromethyl group, difluoromethyl group, trimethylfluoromethyl group, 2,2,2-trifluoroethyl group, pentafluoroethyl group, hepta Examples include a fluoropropyl group. Among these, a monofluoromethyl group, a difluoromethyl group, a trimethylfluoromethyl group, a 2,2,2-trifluoroethyl group, and a pentafluoroethyl group are preferable.

Specific examples of the general formula (2) include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, and ethyl isobutyrate. And aliphatic carboxylic acid esters such as propyl isobutyrate; methyl monofluoroacetate, methyl difluoroacetate, methyl trifluoroacetate, ethyl monofluoroacetate, ethyl difluoroacetate, ethyl trifluoroacetate, trifluoroethyl acetate, tripropionate Examples include fluorine-substituted aliphatic carboxylic acid esters such as fluoroethyl, trifluoroethyl butyrate, and trifluoroethyl isobutyrate. Of these, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl isobutyrate, and ethyl isobutyrate are preferred, and methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate are particularly preferred. Preferred are methyl propionate and ethyl propionate.

[2-4. Composition ratio]
In the non-aqueous electrolyte solution according to the present invention, a non-aqueous organic solvent containing at least one selected from the group consisting of saturated cyclic carbonates, chain carbonates and aliphatic carboxylic acid esters in a total ratio exceeding 90% by volume. Is used. The total ratio is usually 91% or more, preferably 93% or more, more preferably 95% or more, still more preferably 97% or more, particularly preferably 99% or more, and most preferably 100% by volume. Moreover, it is preferable to use a saturated cyclic carbonate and a chain carbonate together, or to use a saturated cyclic carbonate and an aliphatic carboxylic acid ester in combination. The composition ratio (capacity ratio) between the saturated cyclic carbonate and the chain carbonate is usually 5:95 to 50:50, preferably 10:90 to 40:60, and preferably 10:90 to 40:60, from the viewpoint of achieving both conductivity and liquid injection into the electrode. Preferably it is 15: 85-35: 55.

The composition ratio (volume ratio) of the saturated cyclic carbonate and the aliphatic carboxylic acid ester is usually 5:95 to 50:50, preferably 10:90 to 45:55, and more preferably 15:85 to 40:60.
[2-5. Other organic solvents]
The non-aqueous electrolyte solution according to the present invention may contain a solvent other than the above-mentioned cyclic carbonate and chain carbonate having no carbon-carbon unsaturated bond within a range of less than 10% by volume. Examples of such solvents include γ-butyrolactone, α-methyl-γ-butyrolactone, δ-valerolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, N-methylpyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, sulfolane, dimethyl sulfoxide, acetonitrile, trimethyl phosphate, triethyl phosphate, fluorobenzene, 2 , 4-difluorobenzene and at least one selected from trifluoromethylbenzene.

[3. Lithium salt]
The lithium salt is used as an electrolyte, and the type is not particularly limited, and either an inorganic lithium salt or an organic lithium salt may be used.
Examples of inorganic lithium salts include inorganic fluoride salts such as LiPF ₆ , LiAsF ₆ , LiBF ₄ and LiSbF ₆ ; inorganic chloride salts such as LiAlCl ₄ ; perhalogen acids such as LiClO ₄ , LiBrO ₄ and Li IO _4. Examples include salt.

Examples of organic lithium salts include perfluoroalkane sulfonates such as CF ₃ SO ₃ Li and C ₄ F ₉ SO ₃ Li; perfluoroalkane carboxylates such as CF ₃ COOLi; (CF ₃ CO) ₂ Perfluoroalkanecarbonimide salt such as NLi; (CF ₃ SO ₂ ) ₂
Perfluoroalkanesulfonimide salts such as NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi; oxalates such as lithium bis (oxalato) borate (abbreviation: LiBOB), lithium difluorooxalatoborate (abbreviation: LiFOB), etc. Can be mentioned.

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

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

[4. Film-forming agent]
The non-aqueous electrolyte solution according to the present invention further comprises unsaturated cyclic carbonate, monofluorophosphate, difluorophosphate, sultone and sulfite for the purpose of forming a film on the negative electrode and improving battery characteristics. It preferably contains a seed.
The unsaturated cyclic carbonate is not particularly limited as long as it is a cyclic carbonate having a carbon-carbon unsaturated bond, and any one can be used. Specifically, vinylene carbonate, methyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate, fluoro vinylene carbonate, 1,2-difluoro vinylene carbonate, 1-fluoro-2- Vinylene carbonate derivatives such as methyl vinylene carbonate and 1-fluoro-2-phenyl vinylene carbonate; vinyl ethylene carbonate, 1,1-divinyl ethylene carbonate, 1,2-divinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, Examples thereof include vinylethylene carbonate derivatives such as 1-phenyl-2-vinylethylene carbonate and 1-fluoro-2-vinylethylene carbonate.

Among these, vinylene carbonate derivatives such as vinylene carbonate, methyl vinylene carbonate and 1,2-dimethyl vinylene carbonate; vinyl ethylene carbonate derivatives such as vinyl ethylene carbonate and 1,2-divinyl ethylene carbonate are preferable. In particular, vinylene carbonate and vinyl ethylene carbonate are more preferable.
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. If the upper limit of the above range is exceeded, the solubility in the electrolytic solution tends to deteriorate. Further, the molecular weight of the unsaturated cyclic carbonate is usually 80 or more, and usually 250 or less, preferably 150 or less. If the molecular weight is too large, the solubility in the electrolytic solution is deteriorated, and there is a possibility that the effect of the present invention of improving high-temperature storage characteristics cannot be sufficiently exhibited.

  The concentration of the unsaturated cyclic carbonate is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 0.3% by weight or more, and usually 10% by weight or less, preferably based on the whole electrolyte solution. Is 7% by weight or less, more preferably 5% by weight or less, and still more preferably 3% by weight or less. If the concentration of the unsaturated cyclic carbonate is too large, the high-temperature storage characteristics tend to deteriorate, and further, the amount of gas generated increases when the battery is used, and the capacity retention rate may decrease. On the other hand, if the concentration is too small, the effects of the present invention may not be sufficiently exhibited. In addition, when using 2 or more types of unsaturated cyclic carbonate together, it is preferable to make it the total of a density | concentration be in the said range.

Preferred examples of the monofluorophosphate and difluorophosphate include sodium monofluorophosphate, lithium monofluorophosphate, potassium monofluorophosphate, sodium difluorophosphate, lithium difluorophosphate, and potassium difluorophosphate. Further, lithium monofluorophosphate and lithium difluorophosphate are particularly preferable. The concentration of monofluorophosphate and difluorophosphate is generally 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 0.2% by weight or more in total with respect to the whole electrolyte solution. Usually, it is 10 weight% or less, Preferably it is 3 weight% or less, More preferably, it is 2 weight% or less, More preferably, it is 1 weight% or less. If the concentrations of monofluorophosphate and difluorophosphate are too high, the reaction resistance of the negative electrode tends to increase and the capacity tends to decrease. On the other hand, if the concentration is too small, the effects of the present invention may not be sufficiently exhibited.

  Examples of the sultone include 1,3-propane sultone, 1,3-propene sultone, and 1,4-butane sultone, and 1,3-propane sultone and 1,3-propene sultone are particularly preferable. preferable. The total concentration of sultone is usually 0.01% by weight or more, preferably 0.2% by weight or more, more preferably 0.5% by weight or more, and usually 10% by weight or less, preferably 5% in total with respect to the entire electrolyte. % By weight or less, more preferably 3% by weight or less, still more preferably 2% by weight or less. If the sultone concentration is too large, the reaction resistance of the negative electrode tends to increase and the capacity tends to decrease. On the other hand, if the concentration is too small, the effects of the present invention may not be sufficiently exhibited.

  The sulfite is preferably dimethyl sulfite, ethyl methyl sulfite, diethyl sulfite, ethylene sulfite, or propylene sulfite, and ethylene sulfite or propylene sulfite is particularly preferable. The concentration of sulfite is usually 0.01% by weight or more, preferably 0.2% by weight or more, more preferably 0.5% by weight or more, and usually 10% by weight or less, 5% by weight or less, more preferably 3% by weight or less, and still more preferably 2% by weight or less. There is a tendency that the high-temperature storage characteristics where the concentration of sulfite is too high deteriorate. On the other hand, if the concentration is too small, the effects of the present invention may not be sufficiently exhibited.

The film-forming agent is not included in the total amount of the non-aqueous organic solvent defined in claim 1.
[5. 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 acid anhydrides such as maleic anhydride, succinic anhydride, glutaric anhydride; diphenyl disulfide, dimethyl sulfone, divinyl sulfone, 1,4-butanediol dimethane sulfonate, methyl methane sulfonate, methane sulfone Sulfur-containing compounds such as acid-2-propynyl; aromatic compounds such as t-butylbenzene, t-amylbenzene, biphenyl, o-terphenyl, 4-fluorobiphenyl, cyclohexylbenzene, diphenyl ether, and 2,4-difluoroanisole; What substituted this aromatic compound with the fluorine atom etc. are mentioned. Moreover, 1 type may be used independently for an adjuvant, and 2 or more types may be used together by arbitrary combinations and a ratio.

The concentration of the auxiliary agent in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.05% by weight or more, and usually 5% by weight or less, preferably 3% by weight or less. In addition, when using 2 or more types of adjuvants together, it is preferable that the sum of these concentrations falls within the above range. In addition, the said other adjuvant shall not be included as a component of a non-aqueous organic solvent. It is not included in the total of the non-aqueous organic solvents defined in claim 1.

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

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

[7. Method for producing non-aqueous electrolyte]
The non-aqueous electrolyte solution in the present invention is not particularly limited. For example, a lithium salt is added to a non-aqueous organic solvent in which the total proportion of cyclic carbonate and / or chain carbonate having no carbon-carbon unsaturated bond is 95% by volume or more, and further the fluorine-substituted aromatic in the present invention. A group ester compound can be prepared by adding 0.01 to 10% by weight based on the weight of the non-aqueous electrolyte.

  In preparing the non-aqueous electrolyte solution, each raw material of the non-aqueous electrolyte solution, that is, the lithium salt, the non-aqueous solvent, the fluorine-substituted aromatic ester compound in the present invention, and other auxiliary agents may be dehydrated in advance. preferable. As the degree of dehydration, it is desirable to dehydrate until the water content is usually 50 ppm or less, preferably 30 ppm or less. In the present specification, ppm means a ratio based on weight.

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.
The dehydration means is not particularly limited. For example, when the object to be dehydrated is a liquid such as a non-aqueous 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.

[8. 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 fluorine-substituted aromatic ester compound of the present invention is reduced during the initial charging of battery production, and a protective film is formed on the negative electrode. This protective coating has high thermal stability against carbonate solvents. Therefore, when the non-aqueous organic solvent in the electrolytic solution is mainly carbonate and / or aliphatic carboxylic acid ester as in the present invention, the storage characteristics of the battery are improved. However, when the non-aqueous organic solvent in the electrolytic solution contains a large amount other than carbonate or aliphatic carboxylic acid ester as in the known patent document 1, the above-mentioned protective film is easily dissolved in the non-aqueous organic solvent, and the negative electrode As the solvent decomposition reaction proceeds, the storage characteristics deteriorate.

In addition, when the battery is overcharged, the fluorine-substituted aromatic ester compound of the present invention is decomposed at the positive electrode at an early stage of overcharge to generate a gas such as carbon dioxide while generating hydrogen fluoride and / or an oxidation reactant. Is generated. Furthermore, the hydrogen fluoride and / or oxidation reactant produced here act as a catalyst to decompose the carbonate solvent and / or the aliphatic carboxylic acid ester solvent to generate carbon dioxide gas. Therefore, when the non-aqueous organic solvent in the electrolytic solution is mainly carbonate and / or aliphatic carboxylic acid ester solvent as in the present invention, the amount of gas generation is large in the initial stage of overcharge (voltage 5 V). In addition, in a battery equipped with a device that detects the internal pressure and cuts off the current, the current supply can be stopped at a safer stage, so that smoke and fire do not occur. However, when the non-aqueous organic solvent in the electrolytic solution contains a large amount other than carbonate or aliphatic carboxylic acid ester as in known Patent Document 1, the above-described protective coating on the negative electrode is caused by Joule heat generated during overcharge. Since it melt | dissolves and moves to a positive electrode, it decomposes | disassembles and forms a protective film and suppresses decomposition | disassembly of a fluorine substituted aromatic ester compound, The amount of gas to generate | occur | produce becomes inadequate.

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

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

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

Specific examples of transition metal oxides include MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ . As a specific example of the composite oxide of transition metal and lithium, the basic composition is LiN.
Examples include lithium nickel composite oxides such as iO ₂ ; lithium cobalt composite oxides whose basic composition is LiCoO ₂ ; lithium manganese composite oxides whose basic composition is LiMnO ₂ , LiMnO _{4, and the} like. Further, specific examples of the transition metal sulfide include TiS ₂ and FeS.

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

Specifically, _{LiNi 1-ab Mn a Co b} O 2 (a, b represents less than one digit 0 or _{more), LiNi 1-cd Co a} Al d Mg e O 2 (c, d, e is 0 or more less represents a number) is preferably 1, furthermore _{LiNi 1-ab Mn a Co b} O 2 (0 ≦ a <0.4,0 ≦ b <0.4), LiNi 1-cd Co a Al d Mg e O ₂ (0 ≦ c <0.3, 0 ≦ d <0.1, 0 ≦ e <0.05) is preferable, especially LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.85 Co _{0
. 10} Al _0.03 Mg _0.02 O ₂ is preferred.

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

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

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

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

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

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

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

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

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

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

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

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

In addition, these solvents may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.
The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the positive electrode active material.
[1-2. Current collector]
As a material for the current collector, a known material can be arbitrarily used, but usually a metal or an alloy is used. Specifically, examples of the current collector for the positive electrode include aluminum, nickel, and SUS (stainless steel). Among these, aluminum is preferable as the positive electrode current collector. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and ratios.

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

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

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

Usually, as in the case of the positive electrode, a negative electrode having a negative electrode active material layer provided on a current collector is used. Note that, similarly to the positive electrode, the negative electrode may include other layers as appropriate.
[2-1. Negative electrode active material]
The negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium ions, and a known negative electrode active material can be arbitrarily used. For example, it is preferable to use carbonaceous materials such as coke, acetylene black, mesophase micro beads, and graphite; lithium metal; lithium alloys such as lithium-silicon and lithium-tin.

From the viewpoint of high capacity per unit weight and good safety, lithium alloys are particularly preferred, and from the viewpoint of good cycle characteristics and safety, it is particularly preferred to use a carbonaceous material.
In addition, a negative electrode active material may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

Further, the particle size of the negative electrode active material is arbitrary as long as the effects of the present invention are not significantly impaired, but is usually 1 μm or more, preferably 15 μm in terms of excellent battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics. These are usually 50 μm or less, preferably about 30 μm or less.
In addition, for example, those obtained by coating the above carbonaceous material with an organic substance such as pitch and then firing, those obtained by forming amorphous carbon on the surface using the CVD method, etc. It can be suitably used as a quality material. Here, organic substances used for coating include coal tar pitch from soft pitch to hard pitch; coal heavy oil such as dry distillation liquefied oil; straight heavy oil such as atmospheric residual oil and vacuum residual oil; crude oil And heavy petroleum oils such as cracked heavy oil (eg, ethylene heavy end) produced as a by-product during thermal decomposition of naphtha and the like. These heavy oils
The thing which grind | pulverized the solid residue obtained by distilling at 0-400 degreeC to 1-100 micrometers can also be used. Furthermore, a vinyl chloride resin, a phenol resin, an imide resin, etc. can also be used.

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

[2-2. Current collector]
As a material for the current collector of the negative electrode, a known material can be arbitrarily used. For example, a metal material such as copper, nickel, or SUS is used. Among these, copper is particularly preferable from the viewpoint of ease of processing and cost.
The negative electrode current collector is also preferably subjected to a roughening treatment in advance, as with the positive electrode current collector.

Further, like the positive electrode, the shape of the current collector is also arbitrary, and a perforated current collector such as expanded metal or punching metal can also be used. Moreover, the preferable thickness when using a thin film as a current collector is the same as that of the positive electrode.
[3. Spacer]
In order to prevent a short circuit, a spacer is usually interposed between the positive electrode and the negative electrode. The material and shape of the spacer are not particularly limited, but those that are stable with respect to the non-aqueous electrolyte described above, have excellent liquid retention properties, and can reliably prevent short-circuiting between electrodes are preferable.

As a material for the spacer, for example, polyolefin such as polyethylene and polypropylene, polytetrafluoroethylene, polyethersulfone and the like can be used, and polyolefin is preferable.
The spacer is preferably porous. In this case, the non-aqueous electrolyte is used by impregnating a porous spacer.

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

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

Further, when a porous film is used as the spacer, the average pore diameter of the spacer is arbitrary as long as the effect of the present invention is not significantly impaired, but it is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.8. It is 05 μm or more. If it is too large, a short circuit is likely to occur, and if it is too small, the film resistance increases and the rate characteristics may deteriorate.
[4. Assembly of secondary battery]
The lithium secondary battery of the present invention is manufactured by assembling the above-described non-aqueous electrolyte solution according to the present invention, a positive electrode, a negative electrode, and a spacer used as necessary into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary. Furthermore, the shape of the lithium secondary battery of the present invention is not particularly limited, and can be appropriately selected from various shapes generally employed according to the application. For example, a coin-type battery, a cylindrical battery, a square battery, etc. are raised. The method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples and comparative examples, and may be arbitrarily set without departing from the gist of the present invention. It can be implemented with deformation.
<Explanation of test operation>
[Production of positive electrode]
94 parts by weight of lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) which is a positive electrode active material, ₃ parts by weight of polyvinylidene fluoride (hereinafter referred to as “PVdF” as appropriate) and acetylene 3 parts by weight of black was mixed, and N-methylpyrrolidone was added to form a slurry, which was applied to both sides of a current collector made of aluminum and dried to obtain a positive electrode.

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

[Capacity evaluation test]
In a constant temperature bath at 25 ° C., a constant current-constant voltage charge (hereinafter referred to as “CCCV charge” as appropriate) to 4.2 V with a current corresponding to 0.2 C was performed, 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.
[Overcharge characteristics evaluation test]
The battery whose capacity evaluation was completed was CCCV charged to 4.2 V at 0.2 C in a constant temperature bath at 25 ° C. Next, the battery was transferred to a 45 ° C. thermostat, overcharge was started at a current value of 1 C, and the current supply was stopped when 5 V was reached. Then, after cooling the battery to 25 ° C., it was immediately immersed in an ethanol bath and the buoyancy was measured (Archimedes principle) to determine the amount of gas generated.

[Storage characteristics evaluation test]
The battery for which the capacity evaluation was completed 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 85 ° C. for 3 days. Thereafter, the battery was taken out, charged at CCCV to 4.2 V at 0.2 C, 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)
<Example 1>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 2: 7: 1) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Was dissolved at a rate of 1 mol / L, and 4-fluorophenylacetate and vinylene carbonate (VC) were further added so as to be 2% by weight with respect to the total weight of the electrolytic solution, respectively, to obtain a nonaqueous electrolytic solution. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 2>
LiPF ₆ as an electrolyte was added to a mixed solvent (mixing volume ratio 2: 1: 7) with ethylene carbonate (EC) and propylene carbonate (PC), which are saturated cyclic carbonates, and dimethyl carbonate (DMC), which is a chain carbonate. It was dissolved at a rate of 1 mol / L, and 4-fluorophenyl acetate and vinylene carbonate (VC) were further added so as to be 2% by weight with respect to the total weight of the electrolytic solution to obtain a non-aqueous electrolytic solution. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 3>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 2: 7: 1) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Is dissolved at a rate of 1 mol / L, and 4-fluorophenyl acetate and vinylene carbonate (VC) are further added so as to be 4% by weight and 2% by weight, respectively, with respect to the total weight of the electrolytic solution. It was. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 4>
A mixed solvent of ethylene carbonate (EC) and fluoroethylene carbonate (FEC), which are saturated cyclic carbonates, and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), which are chain carbonates (mixing volume ratio 1: 1: 7: In 1), LiPF ₆ that is an electrolyte is dissolved at a rate of 1 mol / L, and 4-fluorophenyl acetate, vinylene carbonate (VC), and vinyl ethylene carbonate (VEC) are each 4 wt. %, 1% by weight and 0.5% by weight were added to obtain a non-aqueous electrolyte. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 5>
A mixed solvent of ethylene carbonate (EC) and fluoroethylene carbonate (FEC), which are saturated cyclic carbonates, and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), which are chain carbonates (mixing volume ratio 1: 1: 7: In 1), LiPF ₆ as an electrolyte was dissolved at a rate of 1 mol / L, and 4-fluorophenyl acetate was further added so as to be 2% by weight with respect to the total weight of the electrolytic solution to obtain a non-aqueous electrolytic solution. . Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 6>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 3: 5: 2) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Is dissolved at a rate of 1 mol / L, and further, 2-fluorophenyl acetate and vinylene carbonate (VC) are added so as to be 2% by weight and 1% by weight, respectively, with respect to the total weight of the electrolytic solution. It was.

Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.
<Example 7>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 3: 5: 2) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Is dissolved at a rate of 1 mol / L, and further, 3-fluorophenyl acetate and vinylene carbonate (VC) are added so as to be 2% by weight and 1% by weight, respectively, with respect to the total weight of the electrolytic solution. It was.

Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.
<Example 8>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 3: 5: 2) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Is dissolved at a rate of 1 mol / L, and 2,4-difluorophenylacetate and vinylene carbonate (VC) are added so as to be 2% by weight and 1% by weight, respectively, with respect to the total weight of the electrolyte solution. An electrolyte was used. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 9>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 3: 5: 2) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Was dissolved at a rate of 1 mol / L, and 2,3,4-trifluorophenylacetate and vinylene carbonate (VC) were added to 2% by weight and 1% by weight, respectively, with respect to the total weight of the electrolyte. Thus, a non-aqueous electrolyte solution was obtained. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 10>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 2: 5: 3) with ethylene carbonate (EC) as a saturated cyclic carbonate and ethyl methyl carbonate (EMC) and diethyl carbonate (DMC) as chain carbonates. Is dissolved at a rate of 1.2 mol / L, and 4-trifluoromethylphenylacetate and vinylene carbonate (VC) are added so as to be 2% by weight with respect to the total weight of the electrolytic solution. It was. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 11>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 2: 5: 3) with ethylene carbonate (EC) as a saturated cyclic carbonate and ethyl methyl carbonate (EMC) and diethyl carbonate (DMC) as chain carbonates. Is dissolved at a rate of 1.2 mol / L, and 3,4-difluorophenylacetate and vinylene carbonate (VC) are further added so as to be 2% by weight with respect to the total weight of the electrolyte solution, respectively, and a non-aqueous electrolyte solution It was. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 12>
Saturated cyclic carbonates ethylene carbonate (EC) and fluoroethylene carbonate (FEC), and chain carbonate dimethyl carbonate (DMC),
In addition, LiPF ₆ as an electrolyte was dissolved at a rate of 1 mol / L in a mixed solvent (mixing volume ratio 1: 1: 2: 5) with ethyl propionate (EP) that is an aliphatic carboxylic acid ester, and 4- Fluorophenyl acetate and vinylene carbonate (VC) were added so as to be 2% by weight with respect to the total weight of the electrolytic solution, respectively, to obtain a non-aqueous electrolytic solution. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 13>
Saturated cyclic carbonates ethylene carbonate (EC) and fluoroethylene carbonate (FEC), and chain carbonate dimethyl carbonate (DMC),
In addition, LiPF ₆ as an electrolyte is dissolved at a rate of 1 mol / L in a mixed solvent (mixing volume ratio 10: 10: 75: 5) with fluorobenzene (PhF) as another organic solvent, and 4-fluorophenyl is further dissolved. Acetate and lithium difluorophosphate (LiPO ₂ F ₂ ) were added so as to be 2% by weight and 0.5% by weight, respectively, with respect to the total weight of the electrolytic solution to obtain a non-aqueous electrolytic solution. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 14>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 2: 7: 1) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Was dissolved at a rate of 1 mol / L, and 4-fluorophenyl acetate and 1,3-propane sultone (PS) were added so as to be 2% by weight and 1% by weight, respectively, with respect to the total weight of the electrolyte. A non-aqueous electrolyte was used. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 15>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 2: 7: 1) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Is dissolved at a rate of 1 mol / L, and further, 4-fluorophenyl acetate and ethylene sulfite (ES) are added so as to be 2% by weight and 1% by weight, respectively, with respect to the total weight of the electrolytic solution, and nonaqueous electrolytic Liquid. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Example 16>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 2: 7: 1) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Is dissolved at a rate of 1 mol / L, and 4-fluorophenyl acetate and 1,3-propene sultone (PRES
) Was added so as to be 2% by weight and 1% by weight, respectively, with respect to the total weight of the electrolytic solution to obtain a non-aqueous electrolytic solution. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Comparative Example 1>
Mixed solvent (mixing volume ratio 2: 7: 1) with saturated cyclic carbonate ethylene carbonate (EC), chain carbonate dimethyl carbonate (DMC), and other organic solvent trimethyl phosphate (TMP) In addition, 1 μm of LiPF ₆ as an electrolyte was added.
1-L was dissolved, and 4-fluorophenyl acetate and vinylene carbonate (VC) were further added so as to be 2% by weight with respect to the total weight of the electrolytic solution to obtain a non-aqueous electrolytic solution.

Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.
<Comparative Example 2>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 2: 7: 1) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Was dissolved at a rate of 1 mol / L, and vinylene carbonate (VC) was further added so as to be 2% by weight with respect to the total weight of the electrolytic solution to obtain a non-aqueous electrolytic solution. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Comparative Example 3>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 2: 7: 1) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Was dissolved at a rate of 1 mol / L, and pentafluorophenyl acetate and vinylene carbonate (VC) were added at 2% by weight with respect to the total weight of the electrolytic solution to obtain a non-aqueous electrolytic solution.
Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

<Comparative Example 4>
LiPF _{6 as} an electrolyte was added to a mixed solvent (mixing volume ratio 2: 7: 1) with ethylene carbonate (EC) as a saturated cyclic carbonate and dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as chain carbonates. Is dissolved at a rate of 1 mol / L, and further, 4-fluorophenyl acetate and vinylene carbonate (VC) are added so as to be 12% by weight and 2% by weight, respectively, with respect to the total weight of the electrolytic solution. It was. Using the obtained non-aqueous electrolyte, a lithium secondary battery was produced according to the above-described method, and a capacity evaluation test, an overcharge characteristic evaluation test, and a storage characteristic evaluation test were performed. The results are shown in Table 1.

表１より、本発明にかかる実施例１〜１６の非水系電解液を用いると、本発明にかかる飽和環状カーボネート、鎖状カーボネート及び脂肪族カルボン酸エステルからなる群から選ばれた少なくとも１種以上を合計割合で９０容量％以下含有する場合（比較例１）や、一般式（１）で表されるフッ素置換芳香族エステル化合物を含有しない場合（比較例２）や、一般式（１）で表されるフッ素置換芳香族エステル化合物とは異なるフッ素置換芳香族エステル化合物を含有する場合（比較例３）や、一般式（１）で表されるフッ素置換芳香族エステル化合物を１０重量％を越えて含有する場合（比較例４）に比べ、安全性と保存特性の両立が可能となることがわかる。すなわち過充電の初期段階（電圧５Ｖ）においてガス発生の量が多いために、内圧を検知して電流を遮断させる装置が備わっている電池においては、より安全な段階で電流供給を停止できるので発煙や発火に至ることがない。また同時に保存特性についても容量維持率の大幅な向上が達成されている。

From Table 1, when using the non-aqueous electrolyte solutions of Examples 1 to 16 according to the present invention, at least one or more selected from the group consisting of saturated cyclic carbonates, chain carbonates and aliphatic carboxylic acid esters according to the present invention. In a total ratio of 90% by volume or less (Comparative Example 1), a case where the fluorine-substituted aromatic ester compound represented by the general formula (1) is not contained (Comparative Example 2), or a general formula (1) When a fluorine-substituted aromatic ester compound different from the fluorine-substituted aromatic ester compound represented (Comparative Example 3) or the fluorine-substituted aromatic ester compound represented by the general formula (1) exceeds 10% by weight It can be seen that both safety and storage characteristics can be achieved in comparison with the case of containing (Comparative Example 4). In other words, since the amount of gas generation is large in the initial stage of overcharge (voltage 5V), in a battery equipped with a device that detects the internal pressure and shuts off the current, the current supply can be stopped at a safer stage, so smoke generation And does not lead to fire. At the same time, the storage characteristics have been greatly improved in capacity retention.

  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)

In a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous organic solvent, the non-aqueous organic solvent is a total of at least one selected from the group consisting of saturated cyclic carbonates, chain carbonates and aliphatic carboxylic acid esters. The fluorine-containing aromatic ester compound represented by the following general formula (1) is contained in an amount of more than 90% by volume and 0.01 to 10% by weight based on the total weight of the non-aqueous electrolyte. Non-aqueous electrolyte.

(In the formula, R ₁ is a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a fluorine atom,
X is a fluorine atom or a C1-C12 fluorine-substituted alkyl group, and n is an integer of 1-4.   The non-aqueous electrolysis according to claim 1, wherein the saturated cyclic carbonate contains at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, monofluoroethylene carbonate, and difluoroethylene carbonate. liquid.   The chain carbonate contains at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate, according to claim 1 or 2. Aqueous electrolyte. The non-aqueous electrolyte solution according to claim 1, comprising at least one selected from the group of compounds represented by the following general formula (2) as the aliphatic carboxylic acid ester.

(In the formula, R ₂ and R ₃ each represent an alkyl group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and each may be the same or different.)   The non-aqueous electrolyte further contains at least one selected from the group consisting of unsaturated cyclic carbonates, monofluorophosphates, difluorophosphates, sultone and sulfites with respect to the total weight of the non-aqueous electrolyte. The nonaqueous electrolytic solution according to any one of claims 1 to 4, wherein the nonaqueous electrolytic solution is contained in an amount of -10% by weight.   A non-aqueous electrolyte battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution is the non-aqueous electrolyte solution according to any one of claims 1 to 5. A lithium secondary battery characterized by that.