JP4835022B2 - Non-aqueous electrolyte and non-aqueous electrolyte battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte battery using the same, and more particularly to a non-aqueous electrolyte secondary battery.
Specifically, the present invention relates to a non-aqueous electrolyte battery that has a high capacity, excellent storage characteristics, cycle characteristics, and continuous charge characteristics, and further generates less gas.

Non-aqueous electrolyte batteries such as lithium secondary batteries are being put to practical use in a wide range of applications from so-called consumer power sources such as mobile phones and laptop computers to in-vehicle power sources for automobiles and the like. However, the demand for higher performance of non-aqueous electrolyte batteries in recent years is increasing, and there is a demand for improvement in battery characteristics.
The electrolyte used for a non-aqueous electrolyte battery is usually composed mainly of an electrolyte and a non-aqueous solvent. As main components of the non-aqueous solvent, cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as dimethyl carbonate and ethyl methyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone are used. Yes.

In addition, in order to improve battery characteristics such as load characteristics, cycle characteristics, storage characteristics, and low temperature characteristics of such nonaqueous electrolyte batteries, various studies have been made on nonaqueous solvents and electrolytes.
For example, when a mixture of asymmetric chain carbonate and a cyclic carbonate having a double bond is used as a non-aqueous solvent, the cyclic carbonate having a double bond preferentially reacts with the negative electrode to form a good film on the negative electrode surface. As a result, formation of a non-conductive film on the negative electrode surface due to the asymmetric chain carbonate is suppressed, and it is known that storage characteristics and cycle characteristics are improved (see Patent Document 1).

  In addition, when a benzene compound having a π electron orbital having a molecular weight of 500 or less and having a reversible redox potential at a potential nobler than the positive electrode potential at the time of full charge is brought into an overcharged state. In this case, it is known that the overcharge current is quickly cut off, the rise in battery temperature is stopped, and the safety and reliability of the battery are improved. It is disclosed that a lithium secondary battery using an electrolytic solution to which 5-difluoroanisole is added maintains high capacity retention after high-temperature storage and suppresses thermal runaway during overcharge (see Patent Document 2). .

Furthermore, it is known that cycle characteristics are improved over a wider temperature range by using an electrolyte containing vinylene carbonate and a methoxybenzene compound such as 4-fluoroanisole or 2,4-difluoroanisole (Patent Document). 3).
Japanese Patent Laid-Open No. 11-185806 Japanese Patent Laid-Open No. 9-50822 JP 2001-338684 A

However, the demand for higher performance of batteries in recent years has been increasing, and it is required to achieve high capacity, high temperature storage characteristics, and cycle characteristics at a high level.
Therefore, as a method for increasing the capacity of a non-aqueous electrolyte battery, it has been studied to pack as much active material as possible in a limited battery volume, and the active material layer of the electrode is pressurized and densified. Design has become commonplace. However, since the voids inside the electrode are reduced by pressurizing and densifying the active material layer of the electrode, the internal pressure of the battery rises remarkably even if a small amount of gas is generated due to the decomposition of the electrolyte. Will occur.

  Moreover, in non-aqueous electrolyte two batteries, in most cases used as a backup power source in the event of a power failure or as a power source for portable devices, a weak current is always supplied to make up for the self-discharge of the battery, and the battery is continuously charged. In such a continuously charged state, the activity of the electrode active material is always high, and at the same time, due to the heat generated by the device, the capacity of the battery is reduced, or the electrolyte is decomposed and gas is easily generated. If a large amount of gas is generated, a safety valve may be activated in a battery that senses this when the internal pressure is abnormally increased due to an abnormality such as overcharge and activates the safety valve. Further, in a battery without a safety valve, the battery may expand due to the pressure of the generated gas, and the battery itself may become unusable.

Therefore, in non-aqueous electrolyte secondary batteries, improvement is required not only for high capacity, high temperature storage characteristics, cycle characteristics, but also for continuous charging characteristics. There is a strong demand to suppress gas generation.
However, the non-aqueous electrolyte secondary battery using the electrolyte described in Patent Documents 1 to 3 is not yet satisfactory in terms of achieving both cycle characteristics, high-temperature storage stability and continuous charge characteristics. It was.

  As a result of various investigations for the electrolyte solution that suppresses gas generation and improves continuous charging characteristics and high-temperature storage characteristics while maintaining high cycle characteristics, the present inventors have an unsaturated bond. By using an electrolytic solution containing a cyclic carbonate and 3,5-difluoroanisole or a similar compound, generation of gas and capacity reduction during continuous charging at high temperatures are suppressed while maintaining high cycle characteristics, The present inventors have found that a decrease in capacity during high-temperature storage is also suppressed, and have completed the present invention.

That is, the gist of the present invention is that in a non-aqueous electrolyte solution containing an electrolyte and a non-aqueous solvent for dissolving the electrolyte, a cyclic carbonate compound in which the non-aqueous electrolyte solution has an unsaturated bond and a compound represented by the following general formula (1) In a non-aqueous electrolyte secondary battery electrolyte.

  (In the formula, R is an alkyl group having 1 to 12 carbon atoms which may be substituted with a fluorine atom, an alkoxyalkyl group having 2 to 12 carbon atoms which may be substituted with a fluorine atom, or a fluorine atom. Represents an optionally substituted phenyl group.)

Another gist is a non-aqueous electrolyte battery including a negative electrode and a positive electrode capable of occluding and releasing lithium ions, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte battery is manufactured using the non-aqueous electrolyte. The present invention resides in a non-aqueous electrolyte secondary battery.

  According to the present invention, it is possible to provide a battery having a high capacity, excellent storage characteristics and cycle characteristics, and capable of suppressing capacity reduction and gas generation during continuous charging. Performance can be achieved.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the description of constituent elements described below is an example (representative example) of an embodiment of the present invention, and is not specified by these contents.
The non-aqueous electrolyte solution according to the present invention contains an electrolyte and a non-aqueous solvent that dissolves the electrolyte, as is the case with conventional non-aqueous electrolyte solutions, and usually contains these as the main components. Here, the main component means that the content of the electrolyte in the non-aqueous electrolyte and the non-aqueous solvent for dissolving the electrolyte is 50% by weight or more.

(Electrolytes)
As the electrolyte, a lithium salt is usually used. The lithium salt is not particularly limited as long as it is known to be used for this purpose, and any lithium salt can be used. Specific examples include the following.
For example, inorganic lithium salts such as LiPF ₆ and LiBF ₄ ; LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,3-perfluoropropane disulfonylimide LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (CF ₃ SO ₂ ) ₂ , LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂ , LiBF ₂ (C ₂ F _And fluorine-containing organic lithium salts such as ₅ SO ₂ ) ₂ and lithium bis (oxalate) borate.

Of these, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ or LiN (C ₂ F ₅ SO ₂ ) ₂ are preferable, and LiPF ₆ or LiBF ₄ is particularly preferable. These lithium salts may be used alone or in combination of two or more.
A preferred example when two or more types are used in combination is a combination of LiPF ₆ and LiBF _{4. In} this case, the proportion of LiBF _{4 in} the total of both is 0.01 wt% or more and 20 wt% or less. It is preferable that it is 0.1 wt% or more and 5 wt% or less.

Another example is the combined use of an inorganic lithium salt and a fluorine-containing organic lithium salt. In this case, the proportion of the inorganic lithium salt in the total of both is 70% by weight or more and 99% by weight or less. It is desirable. The fluorine-containing organic lithium salt is preferably LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , or lithium cyclic 1,3-perfluoropropane disulfonylimide. The combined use of both has an effect of suppressing gas generation during continuous charging and suppressing deterioration due to high temperature storage.

When the non-aqueous solvent contains 55% by volume or more of γ-butyrolactone, the lithium salt is preferably LiBF ₄ or a combination of LiBF ₄ and another. In this case, LiBF ₄ preferably accounts for 40 mol% or more of the lithium salt. Particularly preferably, the proportion of LiBF _{4 in} the lithium salt is 40 mol% or more and 95 mol% or less, and the remainder is LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ is a combination selected from the group consisting of ₂ .

  The concentration of the lithium salt in the non-aqueous electrolyte is usually 0.5 mol / liter or more and 3 mol / liter or less. If the concentration is too low, the electric conductivity of the electrolytic solution is insufficient. If the concentration is too high, the viscosity increases and the electric conductivity is lowered, and the battery performance may be lowered. The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.6 mol / liter or more, and is preferably 1.8 mol / liter or less, particularly preferably 1.5 mol / liter or less.

(Non-aqueous solvent)
The non-aqueous solvent can also be appropriately selected from conventionally known solvents for non-aqueous electrolyte solutions. Examples thereof include cyclic carbonates having no unsaturated bond, chain carbonates, cyclic ethers, chain ethers, cyclic carboxylic acid esters, chain carboxylic acid esters, and phosphorus-containing organic solvents.
Examples of the cyclic carbonates having no unsaturated bond include alkylene carbonates having an alkylene group having 2 to 4 carbon atoms such as ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate, propylene carbonate, and the like. Is preferred.

  Examples of the chain carbonates include dialkyl having an alkyl group having 1 to 4 carbon atoms such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. And carbonates. Among these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable.

Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran.
Examples of chain ethers include dimethoxyethane and dimethoxymethane.
Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone.

Examples of chain carboxylic acid esters include methyl acetate, methyl propionate, ethyl propionate, and methyl butyrate.
Examples of the phosphorus-containing organic solvent include trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, and the like.

These may be used alone or in combination of two or more, but it is preferable to use in combination of two or more. For example, it is preferable to use a high dielectric constant solvent such as alkylene carbonates or cyclic carboxylic acid esters in combination with a low viscosity solvent such as dialkyl carbonates or chain carboxylic acid esters.
One preferable combination of the non-aqueous solvents is a combination mainly composed of alkylene carbonates and dialkyl carbonates. Among them, the total of alkylene carbonates and dialkyl carbonates in the nonaqueous solvent is 85% by volume or more, preferably 90% by volume or more, more preferably 95% by volume or more, and the alkylene carbonates and dialkyl carbonates. The amount of alkylene carbonate with respect to the sum of the above is 5% or more, preferably 10% or more, more preferably 14% or more, usually 50% or less, preferably 35% or less, more preferably 30% or less, still more preferably 25 % Or less. When a non-aqueous electrolyte in which a lithium salt, a cyclic carbonate having an unsaturated bond and a compound represented by the general formula (1) are added to this mixed solvent is used, the balance between cycle characteristics, large current discharge characteristics, and gas generation suppression is achieved. Is preferable.

  Specific examples of preferred combinations of alkylene carbonates and dialkyl carbonates include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate, Examples include ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

A combination in which propylene carbonate is further added to a combination of these ethylene carbonate and dialkyl carbonates is also mentioned as a preferable combination.
When propylene carbonate is contained, the volume ratio of ethylene carbonate to propylene carbonate is usually 99: 1 to 40:60, preferably 95: 5 to 50:50.

  Among these, those containing ethyl methyl carbonate, which is an asymmetric dialkyl carbonate, are more preferable, and in particular, ethylene carbonate and dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate and diethyl carbonate and ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate, Those containing ethylene carbonate, symmetric dialkyl carbonates and asymmetric dialkyl carbonates such as diethyl carbonate and ethyl methyl carbonate are preferred because of a good balance between cycle characteristics and large current discharge characteristics.

  Another example of a preferable non-aqueous solvent is an organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone, or a mixed solvent composed of two or more organic solvents in an amount of 60% by volume. It occupies the above. The non-aqueous electrolyte using this mixed solvent is less likely to evaporate or leak when used at high temperatures. Among these, the total of ethylene carbonate and γ-butyrolactone in the nonaqueous solvent is 80% by volume or more, preferably 90% by volume or more, and the volume ratio of ethylene carbonate and γ-butyrolactone is 5:95 to 45%. : 55, or the total of ethylene carbonate and propylene carbonate in the non-aqueous solvent is 80% by volume or more, preferably 90% by volume or more, and the volume ratio of ethylene carbonate to propylene carbonate is 30:70 to Use of a material having a ratio of 60:40 generally improves the balance between cycle characteristics and large current discharge characteristics.

It is also preferable to use a phosphorus-containing organic solvent as the non-aqueous solvent. When the phosphorus-containing organic solvent is contained in the non-aqueous solvent so as to be usually 5% by volume or more, preferably 10% by volume or more and 80% by volume or less, the flammability of the electrolytic solution can be lowered. In particular, when a phosphorus-containing organic solvent is used in combination with a nonaqueous solvent selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, and dialkyl carbonate, cycle characteristics and large current discharge characteristics This is preferable because the balance is improved.
In the present specification, the capacity of the non-aqueous solvent is a measured value at 25 ° C., but a measured value at the melting point is used for a solid at 25 ° C. such as ethylene carbonate.

(3,5-difluoroanisole and related compounds)
The nonaqueous electrolytic solution according to the present invention contains the above-described electrolyte and a nonaqueous solvent, and further contains a compound represented by the following general formula (1).

  (In the formula, R is an alkyl group having 1 to 12 carbon atoms which may be substituted with a fluorine atom, an alkoxyalkyl group having 2 to 12 carbon atoms which may be substituted with a fluorine atom, or a fluorine atom. Represents an optionally substituted phenyl group.)

Examples of the alkyl group include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, tert-butyl group, pentyl group, cyclopentyl group, and cyclohexyl. A linear or cyclic alkyl group having 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, and particularly preferably 1 to 4 carbon atoms is exemplified, and a linear alkyl group is preferable.
The alkyl group having 1 to 12 carbon atoms substituted with a fluorine atom is a group in which part or all of the hydrogen atoms of the above alkyl group are substituted with a fluorine atom, specifically, a trifluoromethyl group or trifluoroethyl group. Group, pentafluoroethyl group and the like.

Examples of the alkoxyalkyl group include chain alkoxyalkyl groups having 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, particularly preferably 2 to 4 carbon atoms, such as a methoxymethyl group and a 2-methoxyethyl group.
Examples of the phenyl group substituted with a fluorine atom include a 2-fluorophenyl group, a 3-fluorophenyl group, a 4-fluorophenyl group, and a 3,5-difluorophenyl group.
The molecular weight of the compound represented by the general formula (1) is usually 144 or more, usually 750 or less, preferably 350 or less, more preferably 280 or less. If the molecular weight is too large, the solubility in the electrolyte may be significantly reduced.

  Specific examples of the compound of the general formula (1) in which R is an alkyl group having 1 to 12 carbon atoms which may be substituted with a fluorine atom include 1,3-difluoro-5-methoxybenzene (3,5-difluoro Anisole), 1,3-difluoro-5-ethoxybenzene, 1,3-difluoro-5-propoxybenzene, 1,3-difluoro-5-cyclohexyloxybenzene, 1,3-difluoro-5-trifluoromethoxybenzene, etc. As a specific example of the compound of the general formula (1), wherein R is an alkoxyalkyl group having 2 to 12 carbon atoms which may be substituted with a fluorine atom, 1,3-difluoro-5- (methoxymethoxy) benzene , 1,3-difluoro-5- (2-methoxyethoxy) benzene is a general formula in which R is a phenyl group optionally substituted by a fluorine atom Specific examples of the compound of 1), 1,3-difluoro-5-phenoxy benzene.

  Among these, 1,3-difluoro-5-methoxybenzene (3,5-difluoroanisole), 1,3-difluoro-5-ethoxybenzene, 1,3-difluoro-5-propoxybenzene, 1 In general formula (1), R is an unsubstituted alkyl group having 1 to 6 carbon atoms or an unsubstituted phenyl group, such as 1,3-difluoro-5-cyclohexyloxybenzene and 1,3-difluoro-5-phenoxybenzene. More preferably, R in the general formula (1) is an unsubstituted lower alkyl group having 1 to 4 carbon atoms, particularly preferably 1,3-difluoro-5-methoxybenzene (3,5 -Difluoroanisole).

The compound represented by the general formula (1) may be used alone or in combination of two or more.
The content of the compound represented by the general formula (1) in the nonaqueous electrolytic solution is usually 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably 0.5% by weight or more. . At a concentration lower than this, the effect of the present invention is hardly exhibited. On the other hand, if the concentration is too high, the storage characteristics of the battery tend to deteriorate, so the upper limit is 10% by weight, preferably 8% by weight, more preferably 6% by weight, and most preferably 3% by weight.

(Cyclic carbonate having an unsaturated bond)
The nonaqueous electrolytic solution according to the present invention further contains a cyclic carbonate having an unsaturated bond.
Examples of the cyclic carbonate having an unsaturated bond include vinylene carbonate compounds, vinyl ethylene carbonate compounds, methylene ethylene carbonate compounds, and the like.
Examples of the vinylene carbonate-based compound include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, fluorovinylene carbonate, trifluoromethyl vinylene carbonate, and the like.

  Examples of the vinyl ethylene carbonate compound include vinyl ethylene carbonate, 4-methyl-4-vinyl ethylene carbonate, 4-ethyl-4-vinyl ethylene carbonate, 4-n-propyl-4-vinyl ethylene carbonate, 5-methyl-4- Examples include vinyl ethylene carbonate, 4,4-divinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, and the like.

Examples of the methylene ethylene carbonate compound include methylene ethylene carbonate, 4,4-dimethyl-5-methylene ethylene carbonate, 4,4-diethyl-5-methylene ethylene carbonate, and the like.
Among these, vinylene carbonate and vinyl ethylene carbonate are preferable from the viewpoint of improving cycle characteristics, and vinylene carbonate is particularly preferable.

These may be used alone or in combination of two or more.
The ratio of the cyclic carbonate having an unsaturated bond in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably 0.3% by weight or more, and most preferably 0.8%. 5% by weight or more. When there are too few cyclic carbonate compounds which have an unsaturated bond in a molecule | numerator, there exists a possibility that the effect of improving the cycling characteristics of a battery cannot fully be exhibited. On the other hand, if the content of the cyclic carbonate having an unsaturated bond is too large, the amount of gas generated during high-temperature storage tends to increase or the discharge characteristics at low temperatures tend to decrease. %, Preferably 4% by weight, particularly preferably 3% by weight.

The weight ratio between the cyclic carbonate having an unsaturated bond in the molecule and the compound represented by the general formula (1) is usually the former: the latter is 1: 0.1-25, preferably at the stage of preparing the electrolytic solution. Is 1: 0.1-10.
By using an electrolytic solution containing a cyclic carbonate having an unsaturated bond and a compound represented by the general formula (1), the non-aqueous electrolyte battery is continuously charged under high temperature and high voltage conditions while maintaining high cycle characteristics. The reason why the characteristics and storage characteristics are improved is not clear, but is presumed as follows.

  First, the cyclic carbonate having an unsaturated bond undergoes reductive decomposition on the negative electrode during initial charging, thereby forming a stable film on the negative electrode surface and improving cycle characteristics. However, the cyclic carbonate having an unsaturated bond is likely to react with the positive electrode material in a charged state, and in continuous charging in which charging is continued at a constant voltage, the positive electrode activity is always high, so the reaction with the positive electrode material proceeds. Deterioration of the positive electrode active material is promoted or the amount of gas generated is increased. On the other hand, the compound represented by the general formula (1) having a 3,5-difluoro structure is different from other fluoro compounds in that it specifically forms a film on the surface of the positive electrode and has a cyclic carbonate having an unsaturated bond. It seems that contact with the positive electrode can be prevented and an increase in gas generation amount can be suppressed. Moreover, the positive electrode surface coating derived from the compound represented by the general formula (1) is excellent in lithium ion permeability and does not deteriorate the battery characteristics. In addition, the compound represented by the general formula (1) It is presumed that both good cycle characteristics and battery characteristics at high temperatures can be achieved without inhibiting the formation of a cyclic carbonate film having an unsaturated bond.

(Other auxiliaries)
Various auxiliary agents such as conventionally known overcharge inhibitors, deoxidizers, and dehydrators may be added to the non-aqueous electrolyte solution according to the present invention as long as the effects of the present invention are not impaired.
As an overcharge inhibitor, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, Examples thereof include partially fluorinated products of the aromatic compounds such as o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene.

  Of these, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran are preferable. Two or more of these may be used in combination. When two or more kinds are used in combination, in particular, a combination of cyclohexylbenzene and t-butylbenzene or t-amylbenzene, biphenyl, alkylbiphenyl, terphenyl, terphenyl partially hydrogenated product, cyclohexylbenzene, or t-butylbenzene. It is preferable to use together those selected from aromatic compounds not containing oxygen such as t-amylbenzene and those selected from oxygen-containing aromatic compounds such as diphenyl ether and dibenzofuran.

  When the non-aqueous electrolyte contains an overcharge inhibitor, the proportion of the overcharge inhibitor in the liquid is usually 0.1% by weight or more, preferably 0.2% by weight or more, particularly preferably 0.3% by weight. % Or more, most preferably 0.5% by weight or more, and the upper limit is usually 5% by weight or less, preferably 3% by weight or less, particularly preferably 2% by weight or less. By containing an overcharge preventing agent, rupture / ignition of the battery can be suppressed during overcharge or the like.

  In general, these overcharge inhibitors react more easily on the positive electrode and the negative electrode than the solvent components of the electrolyte solution, and thus react at sites with high activity of the electrode even during continuous charging or storage at high temperatures. When the compound reacts, the internal resistance of the battery is greatly increased, or the generation of gas causes the discharge characteristics after continuous charging and the discharge characteristics after high temperature storage to be significantly reduced. In this case, it is possible to suppress a decrease in discharge characteristics.

  Other auxiliaries include carbonate compounds such as fluoroethylene carbonate, trifluoropropylene carbonate, phenylethylene carbonate, erythritan carbonate, spiro-bis-dimethylene carbonate, methoxyethyl-methyl carbonate; succinic anhydride, glutaric anhydride, Carboxylic anhydrides such as maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride and phenylsuccinic anhydride; 2, Spiro compounds such as 4,8,10-tetraoxaspiro [5.5] undecane and 3,9-divinyl-2,4,8,10-tetraoxaspiro [5.5] undecane; ethylene sulfite, 1, 3-propanesulfur , Sulfur compounds such as 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide; 1-methyl-2 -Nitrogen-containing compounds such as pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone and N-methylsuccinimide; heptane, octane, cycloheptane, etc. And fluorinated aromatic compounds such as fluorobenzene, difluorobenzene, hexafluorobenzene and benzotrifluoride. Two or more of these may be used in combination.

The ratio of these auxiliaries in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably 0.2% by weight or more, and the upper limit is usually 5% by weight. Hereinafter, it is preferably 3% by weight or less, particularly preferably 1% by weight or less. By adding these auxiliaries, capacity maintenance characteristics and cycle characteristics after high temperature storage can be improved.
In particular, in the present invention, it is preferable not to contain sulfides in order to sufficiently bring out the properties of the compound represented by the general formula (1). Here, the sulfides mean compounds having a sulfide group or a disulfide group, and more specifically, R ¹ —S—R ² (wherein R ¹ and R ² are independently an alkyl group, an aromatic ring) Represents a group or a heterocyclic group, and these groups may further have a substituent). In particular, it is preferable not to contain sulfides having an oxidation potential of 0.3 V or more, preferably 0.2 V or more, lower than the oxidation potential of the compound represented by the general formula (1).

  When such a compound is present, this compound reacts on the positive electrode surface at an earlier stage than the compound represented by the general formula (1), and the reaction of the compound represented by the general formula (1) is inhibited. The gas generation suppression effect of the present invention tends to be inferior.

(Preparation of electrolyte)
The nonaqueous electrolytic solution according to the present invention is prepared by dissolving an electrolyte, a cyclic carbonate having an unsaturated bond, a compound represented by the general formula (1), and other compounds as necessary in a nonaqueous solvent. be able to. In preparing the non-aqueous electrolyte solution, each raw material is preferably dehydrated in advance. Usually, it is good to dehydrate to 50 ppm or less, preferably 30 ppm or less.

(Lithium secondary battery)
The non-aqueous electrolyte solution according to the present invention is suitable for use as an electrolyte solution for secondary batteries, particularly for lithium secondary batteries among batteries. Hereinafter, a lithium secondary battery according to the present invention using this electrolytic solution will be described.
The lithium secondary battery according to the present invention is the same as the conventionally known lithium secondary battery except that the lithium secondary battery is produced using the electrolytic solution of the present invention. A non-aqueous electrolyte battery containing a liquid is usually obtained by housing a positive electrode and a negative electrode in a case through a porous membrane impregnated with the non-aqueous electrolyte solution according to the present invention. Therefore, the shape of the secondary battery according to the present invention is not particularly limited, and may be any of a cylindrical shape, a square shape, a laminate shape, a coin shape, a large size, and the like. The lithium secondary battery according to the present invention has a small amount of gas generation in the continuous charge state as described above. The abnormal operation of the current interrupting device can be prevented. In addition, in a battery whose outer casing has a thickness of 0.4 mm or less and whose outer casing is mainly made of metal aluminum or aluminum alloy, a problem of battery swelling due to an increase in battery internal pressure is likely to occur. Since lithium secondary batteries generate less gas, it is possible to prevent such problems from occurring.

As the negative electrode active material, a carbonaceous material or metal compound capable of inserting and extracting lithium, lithium metal, lithium alloy, and the like can be used. These negative electrode active materials may be used alone or in combination of two or more. Among these, preferred are carbonaceous materials and metal compounds capable of occluding and releasing lithium.
Among the carbonaceous materials, graphite and graphite whose surface is coated with amorphous carbon as compared with graphite are particularly preferable.

  Graphite preferably has a lattice plane (002 plane) d value (interlayer distance) of 0.335 to 0.338 nm, particularly 0.335 to 0.337 nm, as determined by X-ray diffraction using the Gakushin method. The crystallite size (Lc) determined by X-ray diffraction by the Gakushin method is usually 30 nm or more, preferably 50 nm or more, particularly preferably 100 nm or more. The ash content is usually 1% by weight or less, preferably 0.5% by weight or less, particularly preferably 0.1% by weight or less.

  The graphite surface coated with amorphous carbon is preferably graphite having a d-value of 0.335 to 0.338 nm on the lattice plane (002 plane) in X-ray diffraction as a core material. A carbonaceous material having a larger d-value on the lattice plane (002 plane) in X-ray diffraction than the core material is attached, and the d-value on the lattice plane (002 plane) in X-ray diffraction is greater than that of the core material and the core material The ratio with respect to the carbonaceous material having a large is 99/1 to 80/20 by weight. When this is used, a negative electrode having a high capacity and hardly reacting with the electrolytic solution can be produced.

The particle size of the carbonaceous material is a median diameter measured by a laser diffraction / scattering method and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, most preferably 7 μm or more, and usually 100 μm or less, preferably 50 μm or less, More preferably, it is 40 micrometers or less, Most preferably, it is 30 micrometers or less.
The specific surface area of the carbonaceous material by the BET method is usually 0.3 m ² / g or more, preferably 0.5 m ² / g or more, more preferably 0.7 m ² / g or more, and most preferably 0.8 m ² / g. or more, usually 25.0 m ² / g or less, preferably 20.0 m ² / g, more preferably 15.0 m ² / g or less, and most preferably 10.0 m ² / g or less.

Further, the carbonaceous material is analyzed by Raman spectrum using argon ion laser light, the peak is the peak intensity of the peak P _A in the range of 1570~1620cm ^-1 I _A, in the range of 1300~1400cm ^-1 P If the peak intensity of the _B was I _B, R value represented by the ratio of I _B and _{I a (= I B / I} a) is what is preferably in the range of 0.01 to 0.7. Further, the half width of the peak in the range of 1570～1620Cm ^-1 is, 26cm ^-1 or less, are preferred in particular 25 cm ^-1 or less.

  Examples of metal compounds capable of inserting and extracting lithium include compounds containing metals such as Ag, Zn, Al, Ga, In, Si, Ge, Sn, Pb, P, Sb, Bi, Cu, Ni, Sr, and Ba. These metals are used as simple substances, oxides, alloys with lithium, and the like. In the present invention, those containing an element selected from Si, Sn, Ge and Al are preferred, and oxides or lithium alloys of metals selected from Si, Sn and Al are more preferred.

A metal compound capable of occluding and releasing lithium, or an oxide thereof or an alloy with lithium generally has a larger capacity per unit weight than a carbon material typified by graphite, and therefore requires a higher energy density. It is suitable for a secondary battery.
Examples of the positive electrode active material include materials capable of inserting and extracting lithium, such as lithium transition metal composite oxide materials such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide. These compounds include Li _X CoO ₂ , Li _X NiO ₂ , Li _X MnO ₂ , Li _X Co _{1- y My} O ₂ , Li _X Ni _{1- y My} O ₂ , Li _X Mn _{1- y My} O ₂ or the like, where M is usually at least one selected from Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, V, Sr, Ti, 0.4 ≦ x ≦ 1.2, 0 ≦ y ≦ 0.6, or Li _X Mn _a Ni _b Co _c O ₂ (where 0.4 ≦ x ≦ 1.2, a + b + c = 1) Can be mentioned.

Especially represented by _{Li X Co 1-y M y} O 2, Li X Ni 1-y M y O 2, Li X Mn 1-y M y O 2 , etc., cobalt, nickel, and other part of manganese What is replaced with metal or Li _X Mn _a Ni _b Co _c O ₂ (where 0.4 ≦ x ≦ 1.2, a + b + c = 1, | ab | <0.1) This is preferable because the structure can be stabilized.
The positive electrode active materials may be used alone or in combination.

  As the binder for binding the active material, any material can be used as long as it is a material that is stable with respect to the solvent and the electrolyte used in manufacturing the electrode. For example, fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene, polyolefins such as polyethylene and polypropylene, polymers having unsaturated bonds such as styrene / butadiene rubber, isoprene rubber and butadiene rubber, and copolymers thereof, ethylene-acrylic Examples thereof include acrylic acid polymers such as acid copolymers and ethylene-methacrylic acid copolymers, and copolymers thereof.

The electrode may contain a thickener, a conductive material, a filler and the like in order to increase mechanical strength and electrical conductivity.
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 a metal material such as copper or nickel, and a carbon material such as graphite or carbon black.
The electrode may be manufactured by a conventional method. For example, it can be formed by adding a binder, a thickener, a conductive material, a solvent or the like to a negative electrode or a positive electrode active material to form a slurry, applying the slurry to a current collector, drying it, and then pressing it.

In addition, a material obtained by adding a binder or a conductive material to an active material is roll-formed as it is to form a sheet electrode, a pellet electrode is formed by compression molding, and an electrode is formed on the current collector by a technique such as vapor deposition, sputtering, or plating. A thin film of material can also be formed.
When graphite is used as the negative electrode active material, the density of the negative electrode active material layer after drying and pressing is usually 1.45 g / cm ³ or more, preferably 1.55 g / cm ³ or more, particularly preferably 1.60 g. / Cm ³ or more.

Further, the density after drying and pressing of the positive electrode active material layer is usually 2.0 g / cm ³ or more, preferably 3.0 g / cm ³ or more.
Various types of current collectors can be used, but metals and alloys are usually used. Examples of the current collector for the negative electrode include copper, nickel, and stainless steel, and copper is preferred. Examples of the positive electrode current collector include metals such as aluminum, titanium, and tantalum, and alloys thereof, and aluminum or an alloy thereof is preferable.

A porous film is interposed between the positive electrode and the negative electrode to prevent a short circuit. In this case, the electrolytic solution is used by impregnating the porous membrane. The material and shape of the porous film are not particularly limited as long as it is stable to the electrolytic solution and excellent in liquid retention, and a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene is preferable.
The material of the battery case used in the battery according to the present invention is also arbitrary, and nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, or the like is used.

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 as long as the gist thereof is not exceeded.
In addition, each evaluation method of the battery obtained by the following Example and the comparative example is shown below.
[Capacity evaluation]
A lithium secondary battery is charged to 4.2 V at a constant current corresponding to 0.2 C at 25 ° C. in a state of being sandwiched between glass plates in order to enhance adhesion between electrodes, and then a constant current of 0.2 C Was discharged to 3V. This is done for 3 cycles to stabilize the battery. In the 4th cycle, after charging to 4.2V with a constant current of 0.5C, charging is performed until the current value reaches 0.05C with a constant voltage of 4.2V. The initial discharge capacity was determined by discharging to 3 V at a constant current of 0.2C.
Here, 1C represents a current value for discharging the reference capacity of the battery in one hour, and 0.2C represents a current value of 1/5 thereof.

[Measurement of amount of generated gas and evaluation of continuous charge characteristics]
After the capacity evaluation test was completed, the volume was measured by immersing the battery in an ethanol bath. Then, constant current charging was performed at a constant current of 0.5 C at 60 ° C., and after reaching 4.25 V, constant voltage charging was performed. Switching was performed continuously for one week.
After the battery was cooled, it was immersed in an ethanol bath to measure the volume, and the amount of gas generated from the volume change before and after continuous charging was determined.
After measuring the amount of generated gas, discharge to 3 V at a constant current of 0.2 C at 25 ° C., measure the remaining capacity after the continuous charge test, and after the continuous charge when the discharge capacity before the continuous charge test is 100 The remaining capacity (%) was determined.

[Evaluation of high-temperature storage characteristics]
The battery for which the capacity evaluation test has been completed is charged to 4.2 V at a constant current of 0.5 C at 25 ° C., and then charged to a current value of 0.05 C at a constant voltage of 4.2 V, and then at 85 ° C. Stored for 3 days. After sufficiently cooling the battery, discharge to 3 V at a constant current of 0.2 C at 25 ° C., measure the remaining capacity after the storage test, and the remaining after storage when the discharge capacity before the storage test is 100 The capacity (%) was determined.

[Evaluation of cycle characteristics]
After the capacity evaluation test was completed, the battery was charged at a constant current of 0.5 C to 4.2 V at 25 ° C., and then charged at a constant voltage of 4.2 V until the current value reached 0.05 C. A constant current of 1 C A cycle test was conducted to discharge to 3V. The discharge capacity (%) after 300 cycles when the discharge capacity before the cycle test was taken as 100 was determined.

Example 1
[Manufacture of negative electrode]
The d-value of the lattice plane (002 plane) in X-ray diffraction is 0.336 nm, the crystallite size (Lc) is 652 nm, the ash content is 0.07 wt%, the median diameter by laser diffraction / scattering method is 12 μm, and the ratio by BET method Surface area is 7.5 m ² / g, R value (= I _B / I _A ) determined from Raman spectrum analysis using argon ion laser light is 0.12, and half width of peak in the range of 1570 to 1620 cm ⁻¹ Was mixed with 94 parts by weight of natural graphite powder having a weight of 19.9 cm ⁻¹ and 6 parts by weight of polyvinylidene fluoride, and N-methyl-2-pyrrolidone was added to form a slurry. This slurry was uniformly applied to one side of a 12 μm thick copper foil, dried, and then pressed so that the density of the negative electrode active material layer was 1.6 g / cm ³ to obtain a negative electrode.

[Production of positive electrode]
Mix 85 parts by weight of LiCoO ₂ , 6 parts by weight of carbon black and 9 parts by weight of polyvinylidene fluoride (product name “KF-1000” manufactured by Kureha Chemical Co., Ltd.), and add N-methyl-2-pyrrolidone to make a slurry. After uniformly applying and drying on both surfaces of a 15 μm thick aluminum foil, the positive electrode active material layer was pressed to a density of 3.0 g / cm ³ to obtain a positive electrode.

[Manufacture of electrolyte]
Under a dry argon atmosphere, 97 parts by weight of a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 2: 4: 4), 2 parts by weight of vinylene carbonate and 1 part by weight of 3,5-difluoroanisole were mixed, A sufficiently dried LiPF ₆ was dissolved at a rate of 1.0 mol / liter to obtain an electrolytic solution.

[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 to prepare a battery element. The battery element was inserted into a bag made of a laminate film in which both surfaces of aluminum (thickness: 40 μm) were coated with a resin layer while projecting positive and negative terminals, and then the electrolyte was poured into the bag and vacuum sealed. The sheet-like lithium secondary battery was produced and evaluated.
The components of the electrolytic solution and the evaluation results are shown in Table-1 to Table-3.

(Example 2)
A sheet-like lithium secondary battery was prepared and evaluated in the same manner as in Example 1 except that 96 parts by weight of a mixture of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate and 2 parts by weight of 3,5-difluoroanisole were used. went. The components of the electrolytic solution and the evaluation results are shown in Table-1 to Table-3.

(Example 3)
A sheet-like lithium secondary battery was prepared and evaluated in the same manner as in Example 1 except that 93 parts by weight of a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate and 5 parts by weight of 3,5-difluoroanisole were used. went. The components of the electrolytic solution and the evaluation results are shown in Table-1 to Table-3.

Example 4
A sheet-like lithium secondary battery was prepared and evaluated in the same manner as in Example 1 except that 90 parts by weight of a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate and 8 parts by weight of 3,5-difluoroanisole were used. went. The components of the electrolytic solution and the evaluation results are shown in Table-1 to Table-3.

(Example 5)
A sheet-like lithium secondary battery was prepared and evaluated in the same manner as in Example 1 except that 96.8 parts by weight of a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate and 0.2 part by weight of dimethyl disulfide were used. went. The components of the electrolytic solution and the evaluation results are shown in Table-1 to Table-2.

(Comparative Example 1)
In Example 1, 98 parts by weight of a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate was used, and a sheet-like lithium secondary battery was produced in the same manner except that 3,5-difluoroanisole was not used. Evaluation was performed. The components of the electrolytic solution and the evaluation results are shown in Table-1 to Table-3.

(Comparative Example 2)
In Example 1, a sheet-like lithium secondary battery was prepared and evaluated in the same manner except that 99 parts by weight of a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate was used, and vinylene carbonate was not used. . The components of the electrolytic solution and the evaluation results are shown in Table-1 to Table-3.

(Comparative Examples 3 to 10)
A sheet-like lithium secondary battery was prepared and evaluated in the same manner as in Example 1 except that the compounds shown in Table-1 were used instead of 3,5-difluoroanisole. The components of the electrolytic solution and the evaluation results are shown in Table-1 to Table-2.

(Example 5 / Example using a metal capable of forming an alloy with lithium as the negative electrode active material)
In Example 1, a sheet-like lithium secondary battery was produced and evaluated in the same manner except that the negative electrode and the electrolytic solution obtained by the following method were used. The evaluation results are shown in Table-4.
[Manufacture of negative electrode]
Si powder (average particle size 3 μm) 73 parts by weight, Cu powder (average particle size 2 μm) 8 parts by weight, artificial graphite powder 12 parts by weight, polyvinylidene fluoride 7 parts by weight, N-methyl-2-pyrrolidone was mixed It was made into a slurry, and this slurry was uniformly applied to one side of a copper foil having a thickness of 12 μm, dried and then pressed to obtain a negative electrode.

[Manufacture of electrolyte]
A mixture of 98 parts by weight of a mixture of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate (volume ratio 2: 4: 4), 1 part by weight of vinylene carbonate and 1 part by weight of 3,5-difluoroanisole, and then fully dried LiPF ₆ was dissolved to a ratio of 1.0 mol / liter to obtain an electrolytic solution.

(Comparative Example 11)
A sheet-like lithium secondary battery was prepared and evaluated in the same manner as in Example 5 except that 99 parts by weight of a mixture of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate was used and 3,5-difluoroanisole was not used. Went. The evaluation results are shown in Table-4.

As is apparent from Tables 2 to 4, it can be seen that the battery according to the present invention has a small amount of gas in a continuously charged state, and is excellent in battery characteristics after continuous charging and after high temperature storage, and cycle characteristics. .

Claims (5)

A nonaqueous electrolytic solution containing an electrolyte and a nonaqueous solvent for dissolving the electrolyte, wherein the nonaqueous electrolytic solution contains a cyclic carbonate compound having an unsaturated bond and a compound represented by the following general formula (1) Electrolyte for non-aqueous electrolyte secondary battery .

(In the formula, R is an alkyl group having 1 to 12 carbon atoms which may be substituted with a fluorine atom, an alkoxyalkyl group having 2 to 12 carbon atoms which may be substituted with a fluorine atom, or a fluorine atom. Represents an optionally substituted phenyl group.) The electrolyte solution for nonaqueous electrolyte secondary batteries according to claim 1, wherein R is an unsubstituted alkyl group having 1 to 6 carbon atoms or an unsubstituted phenyl group. The content of the cyclic carbonate compound having an unsaturated bond is 0.01 to 8% by weight,
The content of the compound represented by 1) is 0.01 to 10% by weight , The electrolyte solution for a non-aqueous electrolyte secondary battery according to claim 1 or 2. The electrolyte solution for a non-aqueous electrolyte secondary battery according to claim 1, which does not contain sulfides. 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, wherein the non-aqueous electrolyte battery is the non-aqueous electrolyte according to any one of claims 1 to 4. A non-aqueous electrolyte secondary battery, characterized by being manufactured using a liquid.