JP2003297423A - Nonaqueous system electrolyte solution and nonaqueous system electrolyte solution secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery having improved safety when overcharged and capable of suppressing battery performance degradation after high temperature preservation, and a nonaqueous system electrolyte solution from which the lithium secondary battery can be obtained. <P>SOLUTION: The nonaqueous system electrolyte solution secondary battery comprises negative and positive electrodes capable of storing and releasing lithium and a nonaqueous system electrolyte solution including a solute and organic solvent, wherein the organic solvent contains a sulfone compound of general formula (1) as shown below and an aromatic compound of general formula (2) with a molecular weight equal to or less than 500. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte used therein. More specifically, the present invention relates to a highly reliable non-aqueous electrolyte secondary battery that prevents deterioration of the battery during high temperature storage, and a non-aqueous electrolyte solution for providing the same.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries having high energy density have been attracting attention as electric products have become lighter and smaller. Further, with the expansion of application fields of lithium secondary batteries, improvement of battery characteristics is also demanded. Examples of the solvent for the electrolytic solution of such a lithium secondary battery include high-dielectric constant solvents such as cyclic carbonic acid esters such as ethylene carbonate and propylene carbonate or cyclic carboxylic acid esters such as γ-butyrolactone, diethyl carbonate and carbonic acid. A suitable mixture of low viscosity solvents such as chain carbonic acid esters such as dimethyl or ethers such as dimethoxyethane is used. These non-aqueous solvents are excellent solvents in terms of battery characteristics such as high dielectric constant and high oxidation potential, and thus excellent stability during battery use.

On the other hand, the electrolytic solution using the above non-aqueous solvent is
Since the non-aqueous solvent has high stability and can be used at a high potential, conversely, a so-called overcharge phenomenon in which a voltage becomes equal to or higher than a predetermined upper limit voltage at the time of charging tends to be a problem.
It is important to improve the safety of the secondary battery during overcharging, because overcharging can cause not only deformation and heat generation of the battery but also, in extreme cases, phenomena such as ignition and rupture.

Conventionally, as an attempt to improve the safety during such overcharge, a method of adding an overcharge inhibitor to the electrolytic solution to cut off the current is known. That is, as an overcharge inhibitor, an aromatic compound such as biphenyl having an oxidation potential equal to or higher than the upper limit voltage value of the battery is added to the electrolytic solution, and when the overcharge state occurs, the aromatic compound is oxidatively polymerized. Then, by forming a high resistance coating on the surface of the active material, the overcharge current is suppressed and the progress of overcharge is stopped (for example, JP-A-9-106835).

[0005]

However, the battery to which the overcharge preventing agent such as biphenyl, 3-chlorothiophene, or furan described in JP-A-9-106835 is added is safe in an overcharged state. However, when stored at high temperature in a normal state of charge, the oxidative polymerization reaction, which should proceed during overcharge, gradually progresses, and the resistance of the resulting film causes a significant decrease in battery performance. there were.

Therefore, there has been a demand for an additive that suppresses the reaction of an overcharge inhibitor during high temperature storage, ensures safety during overcharge, and maintains stable performance even after high temperature storage.

[0007]

The present invention has been made in view of the above problems, and an object thereof is to suppress the reaction of a conventional overcharge inhibitor during high temperature storage in a normally charged state, and To improve the battery performance of. As a result of repeated intensive studies to achieve the above-mentioned objects, the present inventors used a specific compound in combination with a conventionally known aromatic compound-based overcharge inhibitor to suppress the reaction of the aromatic compound, The present invention has been completed by finding that deterioration of battery performance after high temperature storage can be improved.

That is, the gist of the present invention is a non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte solution containing a solute and an organic solvent. A non-aqueous electrolyte secondary containing a sulfone compound represented by the following general formula (1) and an aromatic compound represented by the following general formula (2) having a molecular weight of 500 or less in a system solvent. Batteries.

[0009]

[Chemical 9]

(In the formula, R ₁ and R ₂ are each independently an aryl group or an alkyl group which may be substituted with a halogen atom, or an aryl group which may be substituted with an alkyl group or a halogen atom, R ₁ and R ₂ may be bonded to each other to form a cyclic structure which may contain an unsaturated bond.)

[0011]

[Chemical 10]

(In the formula, R _{3 to} R ₈ are each independently a hydrogen atom, a halogen atom, a chain alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, and a carbon atom having 6 to 1 carbon atoms.
It is an aryl group having 2 or an arylcycloalkyl group having 11 to 14 carbon atoms. ) Another aspect of the present invention is a non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte solution containing a solute and an organic solvent. A non-aqueous electrolyte secondary battery comprising a sulfone compound represented by the following general formula (1) and an aromatic compound represented by the following general formula (3) having a molecular weight of 500 or less in a solvent. ,.

[0013]

[Chemical 11]

(Wherein R ₁ and R ₂ are each independently an aryl group or an alkyl group optionally substituted with a halogen atom, or an aryl group optionally substituted with an alkyl group or a halogen atom, R ₁ and R ₂ may be bonded to each other to form a cyclic structure which may contain an unsaturated bond.)

[0015]

[Chemical 12]

(In the formula, R ₉ is a chain alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and R _{10 to} R ₁₄ are respectively Independently a hydrogen atom, a halogen atom, a chain alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms,
Alternatively, it is an aryl group having 6 to 12 carbon atoms, and R ₉ and R ₁₀
~ R ₁₄ may combine with each other to form a cyclic structure. ) Still another subject matter of the present invention is a non-aqueous electrolyte solution for a secondary battery, which is used in combination with a negative electrode and a positive electrode capable of inserting and extracting lithium, and which comprises a solute and an organic solvent. A non-aqueous electrolysis, wherein the organic solvent contains a sulfone compound represented by the following general formula (1) and an aromatic compound represented by the following general formula (2) and having a molecular weight of 500 or less. In the liquid.

[0017]

[Chemical 13]

(In the formula, R ₁ and R ₂ are each independently an aryl group or an alkyl group optionally substituted with a halogen atom, or an aryl group optionally substituted with an alkyl group or a halogen atom, R ₁ and R ₂ may be bonded to each other to form a cyclic structure which may contain an unsaturated bond.)

[0019]

[Chemical 14]

(In the formula, R _{3 to} R ₈ are each independently a hydrogen atom, a halogen atom, a chain alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, and a carbon atom having 6 to 1 carbon atoms.
It is an aryl group having 2 or an arylcycloalkyl group having 11 to 14 carbon atoms. ) Still another subject matter of the present invention is a non-aqueous electrolyte solution for a secondary battery, which is used in combination with a negative electrode and a positive electrode capable of inserting and extracting lithium, and which comprises a solute and an organic solvent. A non-aqueous electrolysis, wherein the organic solvent contains a sulfone compound represented by the following general formula (1) and an aromatic compound represented by the following general formula (3) and having a molecular weight of 500 or less. In the liquid.

[0021]

[Chemical 15]

(In the formula, R ₁ and R ₂ are each independently an aryl group or an alkyl group optionally substituted with a halogen atom, or an alkyl group or an aryl group optionally substituted with a halogen atom, R ₁ and R ₂ may be bonded to each other to form a cyclic structure which may contain an unsaturated bond.)

[0023]

[Chemical 16]

(In the formula, R ₉ is a chain alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and R _{10 to} R ₁₄ are respectively Independently a hydrogen atom, a halogen atom, a chain alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms,
Alternatively, it is an aryl group having 6 to 12 carbon atoms, and R ₉ and R ₁₀
~ R ₁₄ may combine with each other to form a cyclic structure. )

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. Examples of the organic solvent used in the non-aqueous electrolytic solution of the present invention include cyclic carbonates such as propylene carbonate, ethylene carbonate and butylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, tetrahydrofuran. , Cyclic ethers such as 2-methyltetrahydrofuran and tetrahydropyran, chain ethers such as dimethoxyethane and diethoxyethane, γ-
Examples thereof include cyclic carboxylic acid esters such as butyrolactone and γ-valerolactone, and chain carboxylic acid esters such as methyl acetate and methyl propionate. These may be used alone or in admixture of two or more kinds.

In the non-aqueous electrolyte of the present invention, the sulfone compound represented by the general formula (1) and the molecular weight of 500 represented by the general formula (2) or (3) are contained in the electrolyte. It is characterized by containing the following aromatic compounds together. R ₁ and R ₂ in the general formula (1) are each independently an aryl group or an alkyl group which may be substituted with a halogen atom, or an aryl group which may be substituted with an alkyl group or a halogen atom. , R ₁ and R ₂
May be bonded to each other to form a cyclic structure which may contain an unsaturated bond.

R above₁And R₂Alkyl group
Is preferably an alkyl group having 1 to 4 carbon atoms,
Specifically methyl group, ethyl group, propyl group, isopropyl group
Group, butyl group and the like. Of the alkyl group
Examples of the aryl group which can be a substituent include a phenyl group and a naphthalene group.
Examples include futyl group and anthranyl group.
However, a phenyl group is preferable. Also, the substituent of the alkyl group
Possible halogen atoms are fluorine atom and chlorine atom.
Child and bromine atoms are preferred. These substituents are alkyl
A plurality of groups may be substituted, and the aryl group and halo may be substituted.
The gen atom may be substituted together. R above₁as well as
R₂Is a 4-membered ring or more
Yes, it may contain double or triple bonds
Yes. R above₁And R₂A linking group formed by and bound to each other
Is, for example, -CH₂-, -CH₂CH₂-, -CH₂
CH ₂CH₂-, -CH₂CH₂CH₂CH₂-, -CH₂C
H₂CH₂CH₂CH₂-, -CH = CH-, -CH = CH
CH₂-, -CH = CHCH₂CH₂-, -CH₂CH = C
HCH₂-, -CH₂CH₂C≡CCH₂CH₂− Is shown as an example
You can The hydrogen atoms of these linking groups are
Substituted by a halogen group, a halogen atom, an aryl group, etc.
May be.

Specific examples of the sulfone compound represented by the above general formula (1) include dimethyl sulfone, diethyl sulfone, ethylmethyl sulfone, methylpropyl sulfone, ethylpropyl sulfone, diphenyl sulfone, methylphenyl sulfone, ethylphenyl sulfone, Chain sulfones such as dibenzyl sulfone, benzyl methyl sulfone, and benzyl ethyl sulfone, sulfolane, 2-methylsulfolane, 3-methylsulfolane, 2-ethylsulfolane, 3-ethylsulfolane, 2,4-dimethylsulfolane, 3-sulfolen, 3-methylsulfolene, 2-
Examples thereof include cyclic sulfones such as phenylsulfolane and 3-phenylsulfolane, and the above-mentioned chain sulfones and halides of cyclic sulfones.

Among the sulfone compounds represented by the general formula (1), dimethyl sulfone, diethyl sulfone, sulfolane and 3-
Sulforene is preferred. One of these sulfone compounds represented by the general formula (1) may be selected and used, or two or more thereof may be used in combination. The amount of the sulfone compound of the general formula (1) contained in the electrolytic solution is 0.
It is preferably 1 to 5% by weight, and 0.1 to 2% by weight
It is more preferable if it is, and it is still more preferable if it is 0.2 to 1% by weight. If the content is too high, the battery characteristics may be adversely affected, and if the content is too low, a sufficient reaction suppressing effect cannot be obtained.

In the present invention, the sulfone compound represented by the general formula (1) has a molecular weight of 500 or less represented by the general formula (2) or the general formula (3), which is oxidized in the overcharge potential region. When used in combination with an aromatic compound, the effect of preventing overcharge can be obtained and the reaction of the aromatic compound that occurs during high temperature storage at a normal charge potential can be suppressed.

The molecular weight of 500 represented by the general formula (2) or the general formula (3), which is oxidized in the overcharge potential region.
The following aromatic compounds usually have an oxidation potential of 4.3 to
It has a range of 4.9V. Here, the oxidation potential can be measured by the following cyclic voltammetry method. [Measuring method of oxidation potential] 1.6m in diameter with only the bottom exposed
Using an H-type cell in which the working electrode side and the counter electrode side were separated by a glass filter using a platinum wire of m as a working electrode and a lithium metal counter electrode and a reference electrode, ethylene carbonate (EC)
Volume ratio of diethyl carbonate (DEC) to 7: 3
0.15 mmol of an aromatic compound as a sample in an electrolytic solution prepared by dissolving LiPF _{6 in} a mixed solvent of 1 mol / L at a concentration of 1 mol / L.
/ G is added to this cell. Then, the potential of the working electrode is swept to the oxidation side (noble side) at a sweep rate of 20 mV / sec. At this time, the potential at which a current density of 0.5 mA / cm ² flows out is defined as the oxidation start potential. The measurement is conveniently performed at room temperature (around 25 ° C.).

The oxidation potential of the compound measured by the above method is usually 4.9 V or less, preferably 4.7 V or less. If the oxidation potential is too high, the effect of preventing overcharge tends to decrease. However, if the oxidation potential is too low, it may react even when the battery is used under normal conditions to deteriorate the battery characteristics. Therefore, the voltage is usually 4.3 V or higher, preferably 4.4 V or higher, and more preferably 4.5 V or higher. To do.

Molecular weight 500 represented by the above general formula (2)
Examples of the aromatic compound below include biphenyl and 2-
Methylbiphenyl, 3-methylbiphenyl, 4-methylbiphenyl, 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, cyclohexylbenzene, 1-fluoro-2-cyclohexylbenzene,
1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene, 2-cyclohexyltoluene, 3-cyclohexyltoluene, 4-cyclohexyltoluene, o-terphenyl, m-terphenyl, p-terphenyl, 3- Examples thereof include cyclohexylbiphenyl, 1,3-diphenylcyclohexane, 1-cyclohexyl-3-phenylcyclohexane and 1,3-dicyclohexylbenzene.

The aromatic compounds represented by the general formula (2) may be used alone or in combination of two or more. Examples of the aromatic compound represented by the general formula (3) and having a molecular weight of 500 or less include diphenyl ether, 2-phenoxytoluene, 3-phenoxytoluene, 4-phenoxytoluene, bis (2-tolyl) ether, bis (3). -Trill)
Ether, bis (4-tolyl) ether, dibenzofuran, 2,3-benzofuran and the like can be mentioned.

These aromatic compounds represented by the general formula (3) may be used alone or in combination of two or more. The aromatic compound represented by the general formula (2) or the general formula (3) and having a molecular weight of 500 or less is preferably added in a proportion of 0.1 to 10% by weight of the non-aqueous electrolyte solution, and more preferably. Is in the range of 1 to 5% by weight.

In addition to the sulfone compound represented by the general formula (1) and the aromatic compound represented by the general formula (2) or the general formula (3) and having a molecular weight of 500 or less, vinylene carbonate or vinylethylene carbonate. It is preferable to use in combination, because not only more excellent overcharge prevention effect and storage stability can be exhibited, but also the cycle characteristics of the battery can be improved. Vinylene carbonate or vinyl ethylene carbonate is preferably added in a proportion of 0.1 to 10% by weight of the non-aqueous electrolyte solution.

As the solute in the non-aqueous electrolyte of the present invention,
Lithium salt is used. Examples of the lithium salt include L
iClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , Li
B (C ₆ H ₅ ) ₄ , LiCl, LiBr, LiCH ₃ S
O ₃ , LiCF 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 CF ₃₎ may be mentioned _2. These two
You may mix and use 1 or more types. 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 to
It is 2.5M, preferably 0.75 to 1.5M. 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 non-aqueous electrolyte solution of the present invention may further contain other components, if necessary. Such other components include, for example, a coating (SEI) on the surface of the active material of the battery.
Various additives and surfactants for forming the can be mentioned. The non-aqueous electrolyte secondary battery of the present invention has a positive electrode,
It contains a negative electrode and the non-aqueous electrolyte solution. The non-aqueous electrolyte is usually used as a component of the electrolyte layer between the positive electrode and the negative electrode, but if it can improve the safety during overcharge and the high temperature storage stability, it is used anywhere in the battery. Good.

A lithium transition metal composite oxide is preferably used as the positive electrode active material constituting the secondary battery of the present invention. Examples of the lithium transition metal composite oxide include lithium cobalt composite oxides such as LiCoO ₂ and Li
Examples thereof include lithium nickel oxide such as NiO ₂ and lithium manganese oxide such as LiMn ₂ O ₄ . Particularly, a metal composite oxide containing lithium and cobalt and / or nickel as essential components 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.
Substitution with other metal species such as i, Cu, Zn, Mg, Ga, and Zr is preferable because it can be stabilized. A plurality of positive electrode active materials may be used in combination.

The active material of the negative electrode constituting the secondary battery of the present invention may be any material capable of inserting and extracting lithium, but a carbonaceous material is preferable. Examples of the carbonaceous material include thermal decomposition products of organic substances under various thermal decomposition conditions, artificial graphite, natural graphite, and the like. Preferably artificial graphite produced by high temperature heat treatment of graphitizable pitch obtained from various raw materials and other artificial graphite and purified natural graphite such as graphitized mesophase microspheres, graphitized mesophase pitch carbon fiber, or these Materials obtained by subjecting graphite to various surface treatments including pitch are used. The carbonaceous material preferably has a lattice plane (002 plane) d value (interlayer distance) of 0.335 to 0.34 nm, which is 0.335 to 0.337 nm, which is obtained by X-ray diffraction by Gakushin method. Is more preferable. The ash content is preferably 1% by weight or less,
It is more preferably 0.5% by weight or less, and particularly preferably 0.1% by weight or less. In addition, X according to the Gakushin method
The crystallite size (Lc) determined by line diffraction is preferably 30 nm or more, more preferably 50 nm or more, and particularly preferably 100 nm or more. Other active materials capable of inserting and extracting lithium may 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 above-mentioned positive electrode and negative electrode are usually
It contains the above-mentioned active material and a binder. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, isoprene rubber, and butadiene rubber. Furthermore, if necessary, the electrode may contain a conductive material such as a metal material such as copper or nickel, or a carbon material such as graphite or carbon black. Particularly for the positive electrode, it is preferable to include a conductive material.

The method for producing the positive electrode or the negative electrode is not particularly limited. For example, the active material can be produced by adding a binder, a thickener, a conductive material, a solvent and the like to form a slurry, coating the substrate of a current collector, and drying, Further, the active material may be roll-formed as it is to be a sheet electrode, or may be compression-molded to be a pellet electrode. Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and the like.

Examples of the current collector that can be used for the electrode include a negative electrode current collector such as a metal or an alloy such as copper, nickel or stainless steel, preferably copper, and a positive electrode current collector such as aluminum or titanium. Metals or alloys such as tantalum, preferably aluminum and its alloys are mentioned. In the secondary battery of the present invention, a separator is usually interposed between the positive electrode and the negative electrode. The material and shape of the separator to be used are not particularly limited, but a porous sheet or nonwoven fabric made of polyolefin such as polyethylene or polypropylene is used as a material that is stable to an electrolytic solution and has excellent liquid retention. Is preferred.

The method for producing the non-aqueous secondary battery according to the present invention, which comprises at least the above-mentioned negative electrode, positive electrode and non-aqueous electrolyte solution, is not particularly limited, and the production of commonly used non-aqueous secondary batteries is not limited. It can be appropriately selected from among the methods. Further, the shape of the secondary battery of the present invention is not particularly limited, the sheet electrode and the separator is a spiral cylinder type, a pellet electrode and a separator combined inside-out structure cylinder type, a pellet electrode and a separator are laminated. A coin type etc. can be used.

[0045]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. [Fabrication of Positive Electrode] The positive electrode contains 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. , N-methylpyrrolidone mixed in a solvent to make a slurry, and then 20 μ
It was produced by coating one side of an aluminum foil having a diameter of m, drying it, rolling it with a pressing machine, and punching it with a punch having a diameter of 12 mm.

[Preparation of Negative Electrode] For the negative electrode, 95% by weight of graphite (plane spacing: 0.336 nm) as a negative electrode active material and 5% by weight of polyvinylidene fluoride (PVdF) as a binder were mixed with N-.
After mixing in a solvent of methylpyrrolidone to make a slurry, it was applied on one surface of a copper foil having a thickness of 20 μm, dried, and further rolled by a press machine, and punched to have a diameter of 12 mm.

[Assembly of Battery] A lithium secondary battery was manufactured using a CR2032 type coin cell in a dry box in an argon atmosphere. That is, a positive electrode is placed on a positive electrode can, a 25 μm porous polyethylene film is placed thereon as a separator, and a polypropylene gasket is pressed, then a negative electrode is placed, a spacer for thickness adjustment is placed, and then an electrolytic solution is applied. After soaking in the battery,
The negative electrode can was placed and the battery was sealed. In the examples and comparative examples, the capacities of the batteries were as follows: the upper limit of charge was 4.2 V and the lower limit of discharge was 3.
It was designed to be about 4.0 mAh at 0V.

At this time, the ratio of the weight W (c) of the positive electrode active material to the weight W (a) of the negative electrode active material is such that lithium ions released from the positive electrode at the upper limit voltage of normal use of the battery are on the opposite negative electrode. Since it is preferable that lithium metal is not deposited, the capacity ratio Rq between the negative electrode and the positive electrode is 1.1 ≦ Rq.
The weight was determined so that ≦ 1.2. The capacity ratio Rq is Q (a) × W (a) / {Q (c) × W
(C)}. Here, the electric capacity per weight of the positive electrode active material is Q (c) mAh / g under conditions corresponding to the initial charging conditions of the battery, and lithium can be occluded to the maximum without depositing lithium metal. The electric capacity per weight of the negative electrode active material was Q (a) mAh / g. Q (c) and Q (a) were measured by using a positive electrode or a negative electrode as a working electrode, using lithium metal as a counter electrode, and assembling a test cell through a separator in the same electrolytic solution as when assembling the above battery.
That is, at the lowest possible current density 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 battery system, the capacity at which the positive electrode can be charged (release of lithium ions from the positive electrode) and the negative electrode are discharged. It was determined as the capacity (capacity of lithium ions stored in the negative electrode).

[Evaluation of Battery] The battery was evaluated in two types: (i) overcharge test and (ii) high temperature storage test. (I) Overcharge test The overcharge test was performed in the order of (1) initial charge / discharge (capacity confirmation), then (2) full charge operation, and further (3) overcharge test.

At the initial charge / discharge (capacity confirmation), 1C
(4.0 mA) It was charged by the constant current constant voltage method with an upper limit of 4.2 V. The charge was cut 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. Here, 1C represents a current value that can be fully charged in one hour, 0.2C represents a current value that is ⅕ of that current value, and 2C represents a current value that is twice that current value, which represents a current value that can be fully charged.

The full charge operation was performed by the constant current constant voltage method (0.05 mA cut) with an upper limit of 4.2 V. The overcharge test was 4.99 V cut or 3 hr cut at 1 C (whichever was reached first was cut). As an index for checking the superiority or inferiority of the overcharge prevention effect, a value obtained by disassembling the coin cell after overcharge and quantifying Li remaining in the positive electrode by elemental analysis was used as the overcharge depth. When the positive electrode composition after the overcharge test is expressed as Li _x CoO ₂ , the larger x (the positive electrode Li residual amount) is, the less overcharge is progressed, and the overcharge prevention effect is high.

Here, x (remaining amount of positive electrode Li) was determined from the molar ratio of Co and net Li in the positive electrode determined by elemental analysis (ICP emission analysis). Incidentally, the number of moles of the net Li also performs determination of phosphorus in the positive electrode (P) In a similar analysis, which was to be due to LiPF _6, the Li molar number corresponding to LiPF ₆ from total Li moles in the positive electrode I subtracted it. (Ii) High temperature storage test In the high temperature storage test, a battery is manufactured separately from the overcharge test,
(1) Initial charge / discharge (capacity confirmation), then (2) full charge operation, (3) high temperature storage test, and (4) charge / discharge after storage (capacity check after storage).

The initial charge / discharge and full charge operations were performed under the same conditions as in the overcharge test. In the high temperature storage test, the fully charged battery was stored in an oven at 60 ° C. for 7 days. After the storage test, the charge / discharge after storage was left at room temperature for 1 hour to return the temperature of the battery to room temperature, and constant current discharge was performed at 0.2 C to 3.0 V. Further, the battery was charged by a constant current constant voltage method with an upper limit of 1 C (4.0 mA) and 4.2 V, and discharged at a constant current of 0.2 C up to 3.0 V to confirm the capacity after storage. The charge was cut at this time when the current value reached 0.05 mA.

The capacity in storage capacity confirmation after storage is used as an index for observing the storage stability at high temperature. It can be said that the storage capacity with a large capacity has high storage stability at high temperature. Example 1 As an electrolytic solution, lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7 at a concentration of 1 mol / liter. Cyclohexylbenzene at a concentration of 2% by weight and dimethyl sulfone at a concentration of 1% by weight were added to the electrolytic solution.

Evaluation of the lithium secondary battery manufactured by the above method, and L in the electrode after disassembling the battery after overcharging
i analysis was performed. The results are shown in Table-1. Example 2 A lithium secondary battery was evaluated and after overcharge in the same manner as in Example 1 except that cyclohexylbenzene was added as an additive at a concentration of 2% by weight and diethyl sulfone was added at a concentration of 1% by weight. Li analysis in the electrode after disassembling the battery was performed. The results are shown in Table-1.

Example 3 As Example 1, except that cyclohexylbenzene was added as an additive at a concentration of 2% by weight, dimethyl sulfone was added at a concentration of 1% by weight, and vinylene carbonate was added at a concentration of 2% by weight. Then, the lithium secondary battery was evaluated, and the Li in the electrode after disassembling the battery after overcharging was analyzed. The results are shown in Table-1.

Example 4 Evaluation of a lithium secondary battery and overcharge were carried out in the same manner as in Example 1 except that dibenzofuran was added at a concentration of 2% by weight and dimethyl sulfone was added at a concentration of 1% by weight as additives. After that, the battery was disassembled and the Li in the electrode was analyzed. The results are shown in Table-1.

Example 5 As Example 1, except that dibenzofuran was added at a concentration of 2% by weight, dimethyl sulfone was added at a concentration of 1% by weight, and vinylene carbonate was added at a concentration of 2% by weight as additives. The lithium secondary battery was evaluated, and the lithium in the electrode after disassembling the battery after overcharging was analyzed. The results are shown in Table-1.

Comparative Example 1 A lithium secondary battery was evaluated and Li was analyzed in the electrode after disassembling the battery after overcharging in the same manner as in Example 1 except that no additive was added. The results are shown in Table-1. Comparative Example 2 Evaluation of a lithium secondary battery and Li in the electrode after disassembling the battery after overcharging were performed in the same manner as in Example 1 except that cyclohexylbenzene was added as an additive at a ratio of 2% by weight. Analysis was carried out. The results are shown in Table-1. In addition,
The voltage oscillation that seems to be due to a short circuit was observed during overcharge,
The amount of apparent overcharge current increased.

Comparative Example 3 Evaluation of a lithium secondary battery was carried out in the same manner as in Example 1 except that cyclohexylbenzene was added as an additive at a ratio of 2% by weight and vinylene carbonate was added at a ratio of 2% by weight, and After the overcharge, the battery was disassembled and the Li in the electrode was analyzed. The results are shown in Table-1.

Comparative Example 4 Evaluation of a lithium secondary battery was carried out in the same manner as in Example 1 except that dibenzofuran was added in an amount of 2% by weight as an additive. L
i analysis was performed. The results are shown in Table-1. It should be noted that during overcharge, a voltage oscillation that was considered to be due to a short circuit was observed, and the apparent amount of overcharge current increased.

Comparative Example 5 Evaluation of a lithium secondary battery was performed in the same manner as in Example 1 except that dibenzofuran was added in an amount of 2% by weight and vinylene carbonate was added in an amount of 2% by weight as additives. After the battery was charged, the battery was disassembled to analyze Li in the electrode. The results are shown in Table-1.

[0063]

[Table 1]

From Table 1 above, the sulfone compound represented by the general formula (1) and the molecular weight 5 represented by the general formula (2) or the general formula (3) which is oxidized in the overcharge potential region are shown.
By adding together with an aromatic compound of 00 or less, it is possible to improve the safety at the time of overcharge, suppress the reaction of the overcharge additive during high temperature storage, and alleviate the deterioration of the battery performance. Recognize.

[0065]

According to the present invention, not only the safety at the time of overcharging due to the overcharge inhibitor can be improved, but also
Provided is an electrolytic solution capable of suppressing deterioration of battery performance after storage at high temperature.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinichi Kinoshita             3-3-1 Chuo 8-chome, Ami Town, Inashiki District, Ibaraki Prefecture             Within Mitsubishi Chemical Corporation F-term (reference) 5H029 AJ04 AJ12 AK03 AL06 AM03                       AM05 AM07 BJ03 BJ27 DJ16                       DJ17 EJ11 HJ01 HJ02 HJ13                 5H050 AA03 AA10 AA15 BA17 CA08                       CB08 FA17 FA19 HA13

Claims (11)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte solution containing a solute and an organic solvent, wherein the organic solvent contains: A non-aqueous electrolyte secondary battery comprising a sulfone compound represented by the following general formula (1) and an aromatic compound represented by the following general formula (2) having a molecular weight of 500 or less. [Chemical 1] (Wherein, R ₁ and R ₂ are each independently aryl or alkyl group which may be substituted with a halogen atom or an alkyl group or an aryl group which may be substituted by a halogen atom, and R ₁ R _{2 s} may be bonded to each other to form a cyclic structure which may contain an unsaturated bond.) (In the formula, R _{3 to} R ₈ are each independently a hydrogen atom, a halogen atom, a chain alkyl group having 1 to 12 carbon atoms, or 5 to 5 carbon atoms.
It is a cycloalkyl group having 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an arylcycloalkyl group having 11 to 14 carbon atoms. ) 2. A non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte solution comprising a solute and an organic solvent, in the organic solvent, A non-aqueous electrolyte secondary battery comprising a sulfone compound represented by the following general formula (1) and an aromatic compound represented by the following general formula (3) having a molecular weight of 500 or less. [Chemical 3] (Wherein, R ₁ and R ₂ are each independently aryl or alkyl group which may be substituted with a halogen atom or an alkyl group or an aryl group which may be substituted by a halogen atom, and R ₁ R _{2 s} may be bonded to each other to form a cyclic structure which may contain an unsaturated bond.) (In the formula, R ₉ is a chain alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, or 6 to 12 carbon atoms.
Of an aryl group, each of R ₁₀ to R ₁₄ independently represent a hydrogen atom, a halogen atom, chain alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, or 6 to 12 carbon atoms It is an aryl group, and R ₉ and R _{10 to} R ₁₄ may combine with each other to form a cyclic structure. ) 3. In the general formula (1), R ₁ and R ₂ are each independently a phenyl group, an alkyl group having 1 to 4 carbon atoms which may be substituted with a halogen atom, a methyl group or a halogen atom. The non-aqueous system according to claim 1 or 2, which is a phenyl group which may be substituted, and R ₁ and R ₂ may combine with each other to form a cyclic structure which may contain an unsaturated bond. Electrolyte secondary battery. 4. The non-aqueous electrolyte secondary battery according to claim 3, wherein the sulfone compound represented by the general formula (1) is dimethyl sulfone, diethyl sulfone, sulfolane or 3-sulfolen. 5. The non-aqueous electrolyte according to claim 1, wherein the sulfone compound represented by the general formula (1) is contained in a proportion of 0.1 to 5% by weight of the non-aqueous electrolyte solution. Aqueous electrolyte secondary battery. 6. The aromatic compound represented by the general formula (2) or the general formula (3) and having a molecular weight of 500 or less is added in an amount of 0.1 to 10% by weight of the non-aqueous electrolyte solution. Item 6. A non-aqueous electrolyte secondary battery according to any one of Items 1 to 5. 7. The non-aqueous electrolyte secondary battery according to claim 1, wherein vinylene carbonate or vinyl ethylene carbonate is added in a proportion of 0.1 to 10% by weight of the non-aqueous electrolyte. . 8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode contains a lithium transition metal composite oxide. 9. The negative electrode has a lattice plane (00
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 8, which is made of a carbon material having a d value of 2 faces) of 0.335 to 0.340 nm. 10. A non-aqueous electrolyte for a secondary battery, which is used in combination with a negative electrode and a positive electrode capable of inserting and extracting lithium, comprising a solute and an organic solvent in the organic solvent. In addition, the non-aqueous electrolyte solution containing the sulfone compound represented by the following general formula (1) and the aromatic compound represented by the following general formula (2) and having a molecular weight of 500 or less. [Chemical 5] (Wherein, R ₁ and R ₂ are each independently aryl or alkyl group which may be substituted with a halogen atom or an alkyl group or an aryl group which may be substituted by a halogen atom, and R ₁ R _{2 s} may be bonded to each other to form a cyclic structure which may contain an unsaturated bond.) (In the formula, R _{3 to} R ₈ are each independently a hydrogen atom, a halogen atom, a chain alkyl group having 1 to 12 carbon atoms, or 5 to 5 carbon atoms.
It is a cycloalkyl group having 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an arylcycloalkyl group having 11 to 14 carbon atoms. ) 11. A non-aqueous electrolyte for a secondary battery, which is used in combination with a negative electrode and a positive electrode capable of inserting and extracting lithium, comprising a solute and an organic solvent in the organic solvent. In addition, the non-aqueous electrolyte solution containing the sulfone compound represented by the following general formula (1) and the aromatic compound represented by the following general formula (3) and having a molecular weight of 500 or less. [Chemical 7] (Wherein, R ₁ and R ₂ are each independently aryl or alkyl group which may be substituted with a halogen atom or an alkyl group or an aryl group which may be substituted by a halogen atom, and R ₁ R _2's may combine with each other to form a cyclic structure which may contain an unsaturated bond.) (In the formula, R ₉ is a chain alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, or 6 to 12 carbon atoms.
Of an aryl group, each of R ₁₀ to R ₁₄ independently represent a hydrogen atom, a halogen atom, chain alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 12 carbon atoms, or 6 to 12 carbon atoms It is an aryl group, and R ₉ and R _{10 to} R ₁₄ may combine with each other to form a cyclic structure. )