JP2003059533A - Nonaqueous system electrolyte solution and nonaqueous system electrolyte solution secondary battery using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous system electrolyte solution and a nonaqueous secondary battery using same with improved safety when overcharged. SOLUTION: The nonaqueous system electrolyte solution contains at least organic solvent and lithium salt as well as substituted oxazolizene compound as expressed in formula (1). In the formula, R1 denotes an organic group, and A denotes formula (1-1) (In the formula, R2 and R3 denote, each independently, hydrogen atom or a monovalent organic group.) or formula (1-2) (In the formula, R4 denotes a bivalent organic group having two free atomic valences on one atom).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte solution and a non-aqueous electrolyte secondary battery using the same. For more information,
The present invention relates to an electrolytic solution for a non-aqueous secondary battery having improved safety in an overcharged state and a non-aqueous electrolytic solution secondary battery using the electrolytic solution.

[0002]

2. Description of the Related Art Generally, non-aqueous secondary batteries include an electrolyte solution in which an electrolyte such as a lithium salt is dissolved in a non-aqueous solvent having a high dielectric constant and a high oxidation potential such as carbonic acid ester, ether and lactone, and a lithium transition metal. Positive electrode active materials such as complex oxides and negative electrode active materials such as carbon materials are used.

However, in an overcharged state, since lithium ions are desorbed from the positive electrode active material, the active material reacts with the electrolytic solution or lithium metal is deposited on the negative electrode, which becomes dendrite-like (dendritic). It may develop and short-circuit with the positive electrode, which may cause gas generation, heat generation, etc., which may cause deformation due to a sudden increase in internal pressure of the battery, thermal runaway, or rupture.

In order to improve safety during overcharge, an aromatic compound such as biphenyl having an oxidation potential exceeding the upper limit voltage value of the battery is added to the electrolytic solution as an overcharge inhibitor,
A method is known in which an overcharge current is suppressed and the progress of overcharge is stopped by oxidatively polymerizing an aromatic compound in an overcharged state to form a film that inhibits the entry and exit of lithium ions on the surface of an active material. Kaihei 7-302614, Japanese Patent Laid-Open No. 9-50822, Japanese Patent Laid-Open No. 9-106835, Japanese Patent No. 2939469, Japanese Patent No. 29832.
No. 05 publication).

[0005]

However, at present, the above-mentioned overcharge preventing method is not sufficient. For example, the overcharge inhibitors such as biphenyl, 3-chlorothiophene, and furan described in JP-A-9-106835 may adversely affect the battery characteristics,
The terphenyl derivative, which is the overcharge inhibitor described in Japanese Patent No. 2939469, may cause a decrease in battery performance due to its low solubility in an electrolytic solution, and is further described in Japanese Patent No. 2983205. Diphenyl ether, which is an overcharge inhibitor, has a problem that it has a strong irritating odor and is difficult to handle.

Further, the method of using these aromatic compounds as an overcharge preventing agent is such that the battery is ruptured by the gas generated by the oxidation reaction of the aromatic compound, or the electron conductive film generated in the positive electrode is short-circuited with the negative electrode. There is also the possibility that the battery will explode and the battery will explode, leaving a safety issue. For these reasons, a new additive system having an excellent effect of preventing overcharge has been demanded.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to use a novel overcharge inhibitor different from the conventional aromatic overcharge inhibitors. It is to prevent overcharge and improve safety during overcharge. As a result of intensive studies conducted by the present inventors to achieve the above object, an excellent overcharge-preventing effect is exhibited by using a specific compound having a 2-thioxo-4-oxazolidinone skeleton as an overcharge-preventing agent. Based on this finding, the present invention has been completed.

That is, the gist of the present invention is at least an organic solvent, a lithium salt, and the following general formula (1):

[0009]

[Chemical 4]

[In the formula, R ₁ represents an organic group, and A is the following general formula (1-1):

[0011]

[Chemical 5]

(Wherein R ₂ and R ₃ each independently represents a hydrogen atom or a monovalent organic group) or the following general formula (1)
-2):

[0013]

[Chemical 6]

(In the formula, R ₄ represents a divalent organic group having two free valences on one atom). ] It exists in the non-aqueous electrolyte solution containing the substituted oxazolidine compound represented by these.

The second aspect of the present invention resides in a non-aqueous electrolyte secondary battery comprising the above non-aqueous electrolyte and a positive electrode and a negative electrode.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. The organic solvent that constitutes the non-aqueous electrolyte solution of the present invention is appropriately selected from organic solvents such as carbonic acid esters, ethers and lactones. Examples of the carbonic acid ester include cyclic carbonic acid esters such as propylene carbonate (PC) and ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DE).
C), and chain carbonic acid esters such as ethyl methyl carbonate (EMC). Examples of ethers include dimethoxyethane (DME) and diethoxyethane (D
EE) and the like. Examples of the lactone include γ-
Examples include butyrolactone (GBL) and γ-valerolactone.

The above organic solvent preferably contains at least one of carbonic acid ester, ether and lactone, and more preferably contains carbonic acid ester. Also,
These plural types can be used in combination. Particularly preferred are cyclic carbonates such as PC and EC, which are high dielectric constant solvents, or lactones such as GBL, and D, which is a low viscosity solvent.
It is a mixed solvent with a chain carbonic acid ester such as MC, DEC and EMC.

In the present invention, a substituted oxazolidine compound having a 2-thioxo-4-oxazolidinone skeleton represented by the following general formula (1) is contained in the electrolytic solution.

[0019]

[Chemical 7]

[In the formula, R ₁ represents an organic group, and A represents the following general formula (1-1):

[0021]

[Chemical 8]

(Wherein R ₂ and R ₃ each independently represent a hydrogen atom or a monovalent organic group) or the following general formula (1
-2):

[0023]

[Chemical 9]

(In the formula, R ₄ represents a divalent organic group having two free valences on one atom). In the general formula (1), R ₁ represents an organic group, for example, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 6 carbon atoms.
10, an arylalkoxy group having 1 to 4 carbon atoms of an alkoxy group, an arylamino group having 6 to 10 carbon atoms, an amino group,
And a dialkylamino group having 2 to 12 carbon atoms and a diarylamino group having 12 to 20 carbon atoms. Of these organic groups, alkyl groups and arylalkoxy groups are preferred.

The alkyl group having 1 to 6 carbon atoms includes
Examples thereof include a methyl group, an ethyl group and a propyl group. Examples of the arylalkoxy group having 6 to 10 carbon atoms and the alkoxy group having 1 to 4 carbon atoms include a phenylmethoxy group. Examples of the arylamino group having 6 to 10 carbon atoms include phenylamino group. As the dialkylamino group having 2 to 12 carbon atoms,
For example, a dimethylamino group can be mentioned. 12 to 2 carbon atoms
Examples of the diarylamino group of 0 include a diphenylamino group.

In the above general formula (1), A represents a divalent group represented by the general formula (1-1) or (1-2).
The organic group represented by R ₂ and R ₃ in the general formula (1-1) is, for example, an alkyl group having 1 to 6 carbon atoms or 6 to 10 carbon atoms.
An aryl group of, an alkylcarbonyl group having 1 to 6 carbon atoms,
It is selected from the group consisting of a pyridyl group and a fluoropyridyl group. Hydrogen, an alkyl group, and an aryl group are preferable as R ₂ and R ₃ .

As the above-mentioned alkyl group having 1 to 6 carbon atoms,
Examples thereof include a methyl group, an ethyl group and a propyl group. Examples of the aryl group having 6 to 10 carbon atoms include a phenyl group. Examples of the alkylcarbonyl group having 1 to 6 carbon atoms include a methylcarbonyl group and the like. Examples of the fluoropyridyl group include a 2-fluoro-3-pyridyl group and the like.

R ₂ and R ₃ may combine with each other to form a ring structure. The organic group represented by R ₄ in the general formula (1-2) is, for example, a dialkylaminomethylene group having 2 to 12 carbon atoms or a 1-alkyl-2 (1 having 1 to 6 carbon atoms.
H) -Pyridylidene group, 1-alkyl-having 1 to 6 carbon atoms
4 (1H) -pyridylidene group, furylmethylene group, 3-alkyl-2-thiazolidinylidene group having 1 to 6 carbon atoms,
3-alkyl-4-thiazoline-2-ylidene group having 1 to 6 carbon atoms, 3,4,4-trialkyl-2-oxazolidinylidene group having 3 to 18 carbon atoms, and total carbon number of alkyl group 2 12, alkylidene group having 1 to 6 carbon atoms 1- (dialkylamino) alkylidene group, 1 to 6 carbon atoms 1-
Alkyl-2-pyrrolidinylidene group, 3 having 1 to 6 carbon atoms
-Alkyl-2 (3H) -benzothiazolylidene group, 3-alkyl-2 (3H) -benzoxazolilidene group having 1 to 6 carbon atoms, 1,3-dihydro- having 2 to 12 carbon atoms
1,3-Dialkyl-2H-benzimidazole-2-
Ylidene group, arylmethylene group having 6 to 10 carbon atoms, alkoxy group having 1 to 6 carbon atoms, aryl group having 6 to 1 carbon atoms
An alkoxyarylmethylene group of 0, a total carbon number of an alkyl group of 2 to 12, a dialkylaminoarylmethylene group of an aryl group of 6 to 10 carbon atoms, a 1-alkyl-2 (1H) -quinolilidene group of 1 to 6 carbon atoms, Alkyl group total carbon number 2-12, aryl group total carbon number 12-20
1,3-dihydro-1,3-dialkyl-4,5-diaryl-2H-imidazol-2-ylidene group, arylaminomethylene group having 6 to 10 carbon atoms, and aminomethylene group Be done. Among these organic groups, dialkylaminomethylene group, 1-alkyl-2
(1H) -Pyridylidene group, 1-alkyl-4 (1H)
-Pyridylidene group, furylmethylene group, 3-alkyl-
2-thiazolidinylidene group, 3-alkyl-4-thiazoline-2-ylidene group, 3,4,4-trialkyl-2
-Oxazolidinylidene group, 1- (dialkylamino)
Alkylidene group, 1-alkyl-2-pyrrolidinylidene group, 3-alkyl-2 (3H) -benzothiazolilidene group, 3-alkyl-2 (3H) -benzoxazolilidene group, 1,3-dihydro-1, 3-dialkyl-2H-
Benzimidazol-2-ylidene group, arylmethylene group, alkoxyarylmethylene group, dialkylaminoarylmethylene group, 1-alkyl-2 (1H) -quinolilidene group, 1,3-dihydro-1,3-dialkyl-4 A 5,5-diaryl-2H-imidazol-2-ylidene group is preferred.

Examples of the dialkylaminomethylene group having 2 to 12 carbon atoms include dimethylaminomethylene group and the like. 1-alkyl-having 1 to 6 carbon atoms
Examples of the 2 (1H) -pyridylidene group include a 1-methyl-2 (1H) -pyridylidene group. Examples of the 1-alkyl-4 (1H) -pyridylidene group having 1 to 6 carbon atoms include 1-methyl-4 (1H) -pyridylidene group. Examples of the 3-alkyl-2-thiazolidinylidene group having 1 to 6 carbon atoms include a 3-methyl-2-thiazolidinylidene group. Examples of the 3-alkyl-4-thiazoline-2-ylidene group having 1 to 6 carbon atoms include 3-ethyl-
4-thiazoline-2-ylidene group and the like can be mentioned. 3,4,4-trialkyl-2-3 to 18 carbon atoms
Examples of the oxazolidinylidene group include 3,4,4-
Examples thereof include a trimethyl-2-oxazolidinylidene group. Examples of the 1- (dialkylamino) alkylidene group having a total of 2 to 12 carbon atoms in the alkyl group and 2 to 6 carbon atoms in the alkylidene group include 1- (dimethylamino)
Examples thereof include an ethylidene group. Examples of the 1-alkyl-2-pyrrolidinylidene group having 1 to 6 carbon atoms include 1-methyl-2-pyrrolidinylidene group. 3-alkyl-2 (3H) having 1 to 6 carbon atoms
Examples of the benzothiazolilidene group include 3-methyl-
A 2 (3H) -benzothiazolilidene group and the like can be mentioned. Examples of the 3-alkyl-2 (3H) -benzoxazolilidene group having 1 to 6 carbon atoms include 3-methyl-
A 2 (3H) -benzoxazolilidene group and the like can be mentioned. 1,3-dihydro-1,3 having 2 to 12 carbon atoms
Examples of the -dialkyl-2H-benzimidazol-2-ylidene group include a 1,3-dihydro-1,3-dimethyl-2H-benzimidazol-2-ylidene group. Examples of the arylmethylene group having 6 to 10 carbon atoms include a phenylmethylene group and the like. Examples of the alkoxyarylmethylene group having 1 to 6 carbon atoms of the alkoxy group and 6 to 10 carbon atoms of the aryl group include 4-methoxyphenylmethylene group and the like. Examples of the dialkylaminoarylmethylene group having 2 to 12 total carbon atoms of the alkyl group and 6 to 10 carbon atoms of the aryl group include a 4-dimethylaminophenylmethylene group. As the 1-alkyl-2 (1H) -quinolilidene group having 1 to 6 carbon atoms,
For example, 1-ethyl-2 (1H) -quinolilidene group and the like can be mentioned. 2-12 total carbon atoms of the alkyl group,
Examples of the 1,3-dihydro-1,3-dialkyl-4,5-diaryl-2H-imidazol-2-ylidene group having 12 to 20 total carbon atoms of the aryl group include 1,3-
Dihydro-1,3-dimethyl-4,5-diphenyl-2
Examples thereof include H-imidazole-2-ylidene group. Examples of the arylaminomethylene group having 6 to 10 carbon atoms include a phenylaminomethylene group.

Specific examples of the substituted oxazolidine compound used in the present invention include the following compounds. (In the parentheses after the compound name, numbers beginning with A-1 are added.): 3-Ethyl-2-thioxo-4-oxazolidinone (A-1), 3,5,5-trimethyl-2
-Thioxo-4-oxazolidinone (A-2), 3-methyl-5-phenyl-2-thioxo-4-oxazolidinone (A-3), 5-acetyl-3-methyl-2-thioxo-4-oxazolidinone (A -4), 5,5-dimethyl-3- (phenylmethoxy) -2-thioxo-4-
Oxazolidinone (A-5), 5,5-dimethyl-3-
(Phenylamino) -2-thioxo-4-oxazolidinone (A-6), 5- (2-fluoro-3-pyridyl)
-3- (phenylamino) -2-thioxo-4-oxazolidinone (A-7), 5-phenyl-3- (phenylamino) -2-thioxo-4-oxazolidinone (A-
8), 3-amino-5,5-dimethyl-2-thioxo-
4-oxazolidinone (A-9), 5-[(dimethylamino) methylene] -3-ethyl-2-thioxo-4-oxazolidinone (A-10), 3-methyl-5- (1-
Methyl-2 (1H) -pyridylidene) -2-thioxo-
4-oxazolidinone (A-11), 3-ethyl-5
(1-Methyl-4 (1H) -pyridylidene) -2-thioxo-4-oxazolidinone (A-12), 5- (2-
Furylmethylene) -3-methyl-2-thioxo-4-oxazolidinone (A-13), 3-ethyl-5- (3-
Methyl-2-thiazolidinylidene) -2-thioxo-4
-Oxazolidinone (A-14), 3-ethyl-5-
(3-Ethyl-4-thiazoline-2-ylidene) -2-
Thioxo-4-oxazolidinone (A-15), 3-ethyl-5- (3,4,4-trimethyl-2-oxazolidinylidene) -2-thioxo-4-oxazolidinone (A-16), 5- [ 1- (dimethylamino) ethylidene] -3-ethyl-2-thioxo-4-oxazolidinone (A-17), 3-methyl-5- (1-methyl-2-
Pyrrolidinylidene) -2-thioxo-4-oxazolidinone (A-18), 3-ethyl-5- (3-methyl-2)
(3H) -Benzothiazolilidene) -2-thioxo-4
-Oxazolidinone (A-19), 3-ethyl-5-
(3-Methyl-2 (3H) -benzoxazolidene)
-2-thioxo-4-oxazolidinone (A-20),
5- (1,3-dihydro-1,3-dimethyl-2H-benzimidazol-2-ylidene) -3-ethyl-2-
Thioxo-4-oxazolidinone (A-21), 3-methyl-5- (phenylmethylene) -2-thioxo-4-
Oxazolidinone (A-22), 5-[(4-methoxyphenyl) methylene] -3-methyl-2-thioxo-4
-Oxazolidinone (A-23), 5-[(4- (dimethylamino) phenyl) methylene] -3-methyl-2-
Thioxo-4-oxazolidinone (A-24), 5-
(1-Ethyl-2 (1H) -quinolilidene) -3-methyl-2-thioxo-4-oxazolidinone (A-2
5), 5- (1,3-dihydro-1,3-dimethyl-
4,5-Diphenyl-2H-imidazol-2-ylidene) -3-ethyl-3-thioxo-4-oxazolidinone (A-26), 3-ethyl-5-[(phenylamino) methylene] -2- Thioxo-4-oxazolidinone (A-27), 5- (aminomethylene) -3-ethyl-
2-thioxo-4-oxazolidinone (A-28) and the like.

As the substituted oxazolidine compound in the present invention, among the above compounds, (A-1) to (A-
5) and the compounds of (A-10) to (A-26) are more preferable, and the compounds of (A-1) to (A-5) are particularly preferable. Further, the above compounds may be used in combination of plural kinds. The substituted oxazolidine compound used in the present invention is
It is usually 0.0 with respect to the total amount of the organic solvent and the lithium salt.
The amount is 01% by weight or more, preferably 0.005% by weight or more, and more preferably 0.01% by weight or more. On the other hand, the substituted oxazolidine compound is usually a solution saturation amount or less, preferably 10% by weight or less, more preferably 5% by weight or less, based on the total amount of the organic solvent and the lithium salt.
Be compounded. If the content is too large, the internal resistance increases, which may cause a problem that the battery characteristics such as charge / discharge capacity are adversely affected. On the contrary, if the amount is too small, it may not work effectively as an overcharge preventing agent.

In the present invention, by adding the above-mentioned substituted oxazolidine compound to the electrolytic solution, an electrolytic solution having a high effect of preventing overcharge can be obtained. The mechanism of this overcharge prevention has not been fully clarified so far, but is considered as follows. That is, the substituted oxazolidine compound has an appropriate oxidation potential and does not react in the normal operating voltage range of the battery, but it reacts on the positive electrode when the oxidation potential of the positive electrode becomes nobler than usual, such as in an overcharged state. , Li is prevented from coming out of the positive electrode and becoming unstable. On the other hand, in the negative electrode, Li metal is deposited on the negative electrode during overcharge, but if this deposited metal develops into a dendrite form (dendritic form), it causes a short circuit with the positive electrode, which causes gas generation and heat generation, which causes abrupt battery discharge. Increased risk of internal pressure rise, thermal runaway, and burst. It is considered that the substituted oxazolidine compound forms an inorganic or organic film on the negative electrode that is uniform and resistant to heat and the like, thereby suppressing the generation of dendrites on the negative electrode during overcharge.

The electrolytic solution contains a lithium salt as an electrolyte. Examples of the lithium salt include LiClO ₄ , L
iAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C
₆ H ₅ ) ₄ , LiCl, LiBr, LiCH ₃ SO ₃ , Li
_{CF 3 SO 3, LiN (SO} 2 CF 3) 2, LiN (SO 2 C
₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ C
F ₃ ) _{2 and the} like can be mentioned. These may be used as a mixture of two or more. Among the above lithium salts, it is preferable to use LiBF ₄ and LiPF ₆ .
The concentration of the lithium salt is usually 0.5 with respect to the entire electrolytic solution.
~ 1.5M, preferably 0.75 to 1.25M.
If the lithium salt concentration is too high or too low, the electrical conductivity may decrease, and the battery characteristics may be adversely affected.

The electrolytic solution may further contain other components, if necessary. Examples of such components include carbonate compounds having an unsaturated bond such as vinylene carbonate and vinylethylene carbonate, and sultone compounds such as propane sultone and butane sultone. By containing a small amount of these compounds in the electrolytic solution, the charge / discharge cycle characteristics and the storage characteristics in a charged state can be improved. The addition amount is preferably 0.01 to 10% by weight, more preferably 0.1 to 10% by weight.
5% by weight, particularly preferably 0.5 to 4% by weight.

The electrolytic solution of the present invention can be used in a lithium non-aqueous secondary battery. The secondary battery of the present invention comprises a positive electrode, a negative electrode, and the electrolytic solution. The electrolytic solution is usually used as a component of the electrolyte layer between the positive electrode and the negative electrode, but may be used anywhere in the battery as long as it can improve safety during overcharge.

As the positive electrode active material of the positive electrode constituting the secondary battery of the present invention, it is preferable to use a lithium transition metal composite oxide. As the lithium transition metal composite oxide,
LiCoO _{2 and} other lithium cobalt oxides, LiNiO ₂
Examples thereof include lithium nickel oxides, LiMn ₂ O _{4 and} other lithium manganese oxides, and the like. In particular, a lithium-transition metal composite oxide that essentially contains lithium and cobalt and / or nickel is preferable. In these lithium-transition metal composite oxides, a part of the main transition metal element is Al, Ti, V, Cr, Mn, Fe, Co, Li, N.
It can be stabilized by substituting with other metal species such as i, Cu, Zn, Mg, Ga, and Zr. Also,
The positive electrode active material of the positive electrode may be used in combination of plural kinds.

As the negative electrode active material of the negative electrode constituting the secondary battery of the present invention, a substance capable of inserting and extracting lithium can be used, but a carbonaceous substance is preferable. Specific examples of the carbonaceous material include thermal decomposition products of organic substances under various thermal decomposition conditions, artificial graphite, natural graphite, etc., and are produced by high temperature heat treatment of graphitizable pitch obtained from various raw materials. Other artificial graphites such as artificial graphite, graphitized mesophase spherules, graphitized mesophase pitch-based carbon fibers and purified natural graphite, and those obtained by subjecting the graphite to various surface treatments with components containing pitch are preferred.

These carbonaceous materials preferably have a d-value (interlayer distance) of the lattice plane (002 plane) of 0.335 to 0.34 nm, which is determined by X-ray diffraction by Gakushin method.
It is more preferably 335 to 0.337 nm. In addition, the crystallite size (L
c) is preferably 30 nm or more, more preferably 50 nm or more, and particularly preferably 100 nm or more.

Other active materials capable of occluding and releasing lithium can be further mixed with these carbonaceous materials and used.
Examples of the active material capable of inserting and extracting lithium other than carbonaceous materials include metal oxide materials such as tin oxide and silicon oxide, lithium metal, and various lithium alloys. You may use these negative electrode materials in mixture of 2 or more types.

The method for producing the electrode is not particularly limited, and a known method can be used. For example, a method of producing a slurry by adding a binder, a thickener, a conductive material, a solvent, etc. to the active material of each electrode, coating the substrate of a current collector, and drying the active material, There is a method in which a sheet electrode is formed by roll molding as it is, and a pellet electrode is formed by compression molding.

Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, isoprene rubber, and butadiene rubber. Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch and casein.

Examples of the conductive material include metal materials such as copper and nickel, and carbon materials such as graphite and carbon black. Regarding the current collector used for the electrode, examples of the negative electrode current collector include metals or alloys such as copper, nickel and stainless steel, and among these, copper is preferable. Examples of the positive electrode current collector include metals and alloys such as aluminum, titanium and tantalum among these, and among these, aluminum and its alloys are preferable.

The separator used in the secondary battery of the present invention may be any that is stable to the electrolytic solution and has an excellent liquid retention property. For example, a polyolefin such as polyethylene or polypropylene is used as a raw material. Examples include porous sheets and non-woven fabrics. The shape of the secondary battery of the present invention is not particularly limited, and is a cylinder type having a sheet electrode and a separator in a spiral shape, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, Examples include a coin type in which a pellet electrode and a separator are laminated.

The method for producing the non-aqueous secondary battery according to the present invention composed of the positive electrode, the negative electrode and the non-aqueous electrolytic solution is not particularly limited, and may be appropriately selected from the commonly used methods. it can.

[0045]

EXAMPLES Hereinafter, specific modes of the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples unless the gist thereof is exceeded. [Production of Positive Electrode] 90% by weight of lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material, 5% by weight of acetylene black as a conductive agent, and 5% by weight of polyvinylidene fluoride (PVdF) as a binder in N-methylpyrrolidone. The mixture obtained in (1) and made into a slurry was applied to one side of an aluminum foil having a thickness of 20 μm and dried. Roll this with a press machine,
A positive electrode was prepared by punching with a punch having a diameter of 12 mm. [Fabrication of Negative Electrode] Graphite (plane spacing 0.33) as a negative electrode active material.
(6 nm) 95 wt% and polyvinylidene fluoride (PVdF) 5 wt% as a binder were mixed in N-methylpyrrolidone, and the slurry was applied to one side of a copper foil having a thickness of 20 μm and dried. . This was rolled with a press and punched with a punch having a diameter of 12.5 mm to produce a negative electrode. [Battery assembly] In a dry box in an argon atmosphere,
A CR2032 type coin cell was used to produce a lithium secondary battery by the following method.

First, the positive electrode was placed on the positive electrode can, and two 25 μm-thick porous polyethylene films were placed thereon as separators. After pressing this with a polypropylene gasket, the negative electrode was placed and a spacer for adjusting the thickness was placed. Next, an electrolytic solution was added, and the solution was sufficiently impregnated into the battery, and then the negative electrode can was placed on the battery to seal the battery. The reason for using two separators is to prevent lithium in the negative electrode from mixing with the positive electrode when elemental analysis is performed after overcharging, which will be described later.

In Examples and Comparative Examples, the battery capacity was about 4.3 m when the upper limit of charging was 4.2 V and the lower limit of discharging was 3.0 V.
The amount of the active material of the electrode was designed to be Ah. Therefore, the reference current amount (1
C) was set to 4.3 mA. Further, the range of the capacity ratio Rq between the negative electrode and the positive electrode is 1.1 ≦, which is a range in which lithium ions released from the positive electrode at the upper limit voltage during normal use of the battery do not cause deposition of lithium metal on the facing negative electrode. Rq ≦ 1.
The ratio of the weight W (c) of the positive electrode active material and the weight W (a) of the negative electrode active material was determined so as to be 2. The capacity ratio Rq
Was calculated by the following formula (A).

[0048]

## EQU1 ## Rq = Q (a) × W (a) / {Q (c) × W (c)} (A) (where Q (c) is the condition corresponding to the initial charge condition of the battery Electric capacity per unit weight of the positive electrode active material (mAh /
g), and Q (a) represents the electric capacity per unit weight (mAh / g) of the negative electrode active material capable of maximally occluding lithium without depositing lithium metal. ) Using a positive electrode or a negative electrode as a working electrode and lithium metal as a counter electrode,
In the electrolytic solution used for battery fabrication and assembly, a test cell was assembled through a separator and Q (c) and Q (a) were measured.
That is, up to the upper limit potential of the positive electrode or the lower limit potential of the negative electrode corresponding to the target initial charging conditions of the target battery system, the capacity at which the positive electrode can be charged (release of lithium ions from the positive electrode) and the negative electrode at the lowest possible current density. Q (c) and Q as the capacity that can be discharged (storing lithium ions in the negative electrode)
When (a) was determined, in the electrodes used in this example and the comparative example, the negative electrode Q (a) was about 380 mAh / g and the positive electrode Q (c) was about 155 mAh / g. [Evaluation of Battery] The battery was evaluated by performing (1) initial charge / discharge (capacity confirmation), (2) full charge operation, and (3) overcharge test in this order.

In the initial charge / discharge (capacity confirmation), 1C (4.
3 mA), and the battery was charged by the constant current constant voltage method with an upper limit of 4.2 V. Charging was stopped when the current value reached 0.05 mA. The discharge was performed at a constant current of 0.2 C up to 3.0 V. The full charge operation was performed by a constant current constant voltage method (0.05 mA cut) with an upper limit of 4.2 V.

The overcharge test was stopped at 4.99V at 1C or 3 hours, whichever came first. The effect of preventing overcharge was determined by the following method. That is, after overcharging, the coin cell was disassembled, and the lithium remaining in the positive electrode was quantified by elemental analysis, and this value was taken as the overcharge depth. When the positive electrode composition after the overcharge test is represented by Li _x CoO ₂ , the larger the x (remaining amount of positive electrode lithium), the higher the overcharge prevention effect.

Here, x (remaining amount of positive electrode lithium) was determined from the molar ratio of cobalt and net lithium in the positive electrode determined by elemental analysis (ICP emission analysis). The net number of moles of lithium was also determined by the same analytical method as the amount of phosphorus (P) in the positive electrode, and this was determined by LiPF ₆ , and the total number of moles of lithium in the positive electrode was used to determine the number of moles of lithium corresponding to LiPF _6. Was calculated by subtracting.

Even if the positive electrode lithium remaining amount x is large, it is considered that there is a safety problem when the battery is short-circuited. Therefore, to estimate the degree of short circuit,
While observing the voltage curve at the time of overcharging, providing a rest time of 1 hour after the end of the overcharge test, and measuring the open circuit voltage at the end of the rest (hereinafter referred to as "OCV after the test"),
The presence or absence of a short circuit was judged. Example 1 1 mol / mol in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7.
Lithium hexafluorophosphate (LiP
F ₆ ) was dissolved and 3-ethyl-2-thioxo-4 was added to it.
A lithium secondary battery was prepared by using 2% by weight of oxazolidinone as an electrolyte. Example 2 In a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3: 7, 1 mol /
Lithium hexafluorophosphate (LiP
F ₆ ) was dissolved and 3-ethyl-2-thioxo-4 was added to it.
2% by weight of oxazolidinone and 2 of vinylene carbonate
A lithium secondary battery was prepared by using the electrolyte solution containing 1% by weight of the electrolyte solution. Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1 except that 3-ethyl-2-thioxo-4-oxazolidinone was not added. Comparative Example 2 A lithium secondary battery was produced in the same manner as in Example 2 except that 3-ethyl-2-thioxo-4-oxazolidinone was not added. Comparative Example 3 A lithium secondary battery was produced in the same manner as in Example 1 except that 2% by weight of biphenyl was added instead of 3-ethyl-2-thioxo-4-oxazolidinone and vinylene carbonate.

The lithium secondary batteries thus produced were evaluated. The results are shown in Table-1.

[0054]

[Table 1]

As shown in Table 1, when 3-ethyl-2-thioxo-4-oxazolidinone was added (Examples 1-2), when not added (Comparative Examples 1- 2).
Compared to 2), the safety can be improved by suppressing the escape of lithium from the positive electrode in the overcharged state. In Comparative Example 3, the loss of lithium from the positive electrode can be suppressed, but the voltage after overcharging and rest is about 100 to 200 mV lower than the others, and it is determined that a short circuit has occurred in the overcharged state. It is not preferable for safety.

It should be noted that there is no significant difference in normal battery characteristics such as initial characteristics and output characteristics between the lithium secondary battery manufactured in the example and the lithium secondary battery manufactured in the comparative example. It was confirmed that the normal characteristics were not adversely affected.

[0057]

According to the present invention, a non-aqueous electrolyte solution and a non-aqueous secondary battery using the same, which does not use an aromatic compound that causes deterioration during high temperature storage and has improved safety during overcharge, are provided. Can be provided.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenji Okahara             1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa             Within Mitsubishi Chemical Corporation F term (reference) 5H029 AJ12 AK03 AK18 AL02 AL06                       AL07 AL12 AL18 AM03 AM04                       AM05 AM07 CJ08 HJ01 HJ02                 5H050 AA15 BA15 CA08 CA09 CA29                       CB07 CB08 CB12 CB29 GA10                       HA01 HA02

Claims (11)

[Claims] 1. At least an organic solvent, a lithium salt and the following general formula (1): [In the formula, R ₁ represents an organic group, and A represents the following general formula (1-
1): (In the formula, R ₂ and R ₃ are each independently a hydrogen atom or 1
Represents a valent organic group. ) Or the following general formula (1-2): (In the formula, R ₄ represents a divalent organic group having two free valences on one atom.) ] The non-aqueous electrolyte solution containing the substituted oxazolidine compound represented by these. 2. The non-aqueous electrolyte solution according to claim 1, wherein in the general formula (1), R ₁ is an alkyl group. 3. In the general formula (1), A is the general formula (1
The non-aqueous electrolyte solution according to claim 1 or 2, which is represented by -1). 4. The non-aqueous electrolyte solution according to claim 2, wherein the substituted oxazolidine compound represented by the general formula (1) is 3-ethyl-2-thioxo-4-oxazolidinone. 5. The substituted oxazolidine compound represented by the general formula (1) is contained in the range of 0.001% by weight to the saturated amount of dissolution based on the total amount of the organic solvent and the lithium salt. The non-aqueous electrolyte solution according to any one of 1 to 4. 6. The non-aqueous electrolyte solution according to claim 1, further comprising an unsaturated bond-containing carbonate compound. 7. The non-aqueous electrolyte solution according to claim 1, further containing a sultone compound. 8. A non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte according to claim 1 and a positive electrode and a negative electrode. 9. The non-aqueous electrolyte secondary battery according to claim 8, wherein the positive electrode active material of the positive electrode is a lithium transition metal composite oxide. 10. The lithium transition metal composite oxide is selected from the group consisting of lithium cobalt oxide, lithium nickel oxide and lithium manganese oxide.
The non-aqueous electrolyte secondary battery according to. 11. The negative electrode active material of the negative electrode is a carbonaceous material,
The non-aqueous electrolyte secondary battery according to claim 8.