JP2004259697A - Nonaqueous electrolyte and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery having high capacity, excellent preservation characteristics, load characteristics, and cycle characteristics while reducing gas generation, and to provide a nonaqueous electrolyte. <P>SOLUTION: The nonaqueous electrolyte is mainly composed of lithium salt and nonaqueous solvent for dissolving the lithium salt, and contains a compound represented by formula 1. In formula 1, R<SB>1</SB>-R<SB>3</SB>are each independently a 1-12C alkyl group which may be substituted with fluorine atom, a 2-12C alkenyl group which may be substituted with fluorine atom or a 6-12C aryl group which may be substituted with fluorine atom, or a 7-12C aralkyl group which may be substituted with fluorine atom. R<SB>2</SB>and R<SB>3</SB>may combine together to form a nitrogenous alicyclic ring, and R<SB>1</SB>and R<SB>2</SB>may combine together to form a ring structure. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte battery and a non-aqueous electrolyte used therein. More specifically, the present invention relates to a non-aqueous electrolyte battery having high capacity and excellent storage characteristics, load characteristics, and in the case of a secondary battery, excellent cycle characteristics. The present invention also relates to a non-aqueous electrolyte battery that generates a small amount of gas.

With the reduction in weight and size of electric products in recent years, development of lithium batteries having a high energy density has been promoted. Further, as the application field of lithium batteries is expanded, there is a demand for improvement of the battery characteristics. As the negative electrode of the lithium battery, lithium metal, a metal compound capable of occluding and releasing lithium (such as a simple metal, an oxide, and an alloy with lithium), and a carbonaceous material are used.
In particular, a non-aqueous electrolyte secondary battery using a carbonaceous material capable of occluding and releasing lithium such as coke, artificial graphite, and natural graphite has been proposed. In such a nonaqueous electrolyte secondary battery, since lithium does not exist in a metallic state, formation of dendrites is suppressed, and battery life and safety can be improved. In particular, non-aqueous electrolyte secondary batteries using graphite-based carbonaceous materials such as artificial graphite and natural graphite have been receiving attention as meeting the demand for higher capacity.

Further, in order to improve characteristics such as load characteristics, cycle characteristics, storage characteristics, and low-temperature characteristics of non-aqueous electrolyte secondary batteries, electrolytes containing various compounds in addition to an electrolyte and a main solvent have been proposed. . For example, Patent Document 1 discloses an electrolyte characterized by containing a compound having an NS structure in which nitrogen and sulfur are bonded to each other to improve cycle characteristics and storage characteristics, in which the molecular weight is less than 500.
JP-A-2002-280063

  Further, when the battery is used as a backup power supply at the time of a power failure or as a power supply for a portable device, continuous charging is performed in which a weak current is constantly supplied to compensate for self-discharge of the battery and is maintained in a charged state. In such a continuous charge state, the activity of the electrode is always high, so that the capacity deterioration of the battery is promoted, and gas is generated by decomposition of the electrolytic solution. When the amount of generated gas is large, the safety valve may be activated in a cylindrical battery that operates the safety valve by sensing the internal pressure when an abnormality such as overcharging occurs. In the case of a rectangular battery or the like without a safety valve, the battery may be blistered or even exploded.

Therefore, it is required to improve not only high capacity, high temperature storage characteristics, load characteristics, and cycle characteristics but also continuous charging characteristics. As the continuous charging characteristics, it is strongly required not only that the capacity is not deteriorated but also that gas generation is suppressed.
However, 1,1′-sulfonyldiimidazole, N-bismethylthiomethylene-p-toluenesulfonamide and 1-p-tolylsulfonylpyrrole disclosed in Patent Document 1 have storage characteristics at relatively high temperatures of 80 ° C. or higher. And the continuous charging characteristics cannot be improved together.

The present inventors have conducted various studies in order to achieve the above object, and as a result, have found that the above problems can be solved by including a specific compound in an electrolytic solution, thereby completing the present invention. .
That is, the gist of the present invention is to provide a non-aqueous electrolyte solution battery including an anode and a cathode, and an electrolyte solution comprising a non-aqueous solvent and a lithium salt, wherein the non-aqueous electrolyte solution further contains a compound represented by the general formula (1). A non-aqueous electrolyte battery.

(Wherein, R _{1 to} R ₃ each independently represent an alkyl group having 1 to 12 carbon atoms which may be substituted with a fluorine atom, or an alkenyl having 2 to 12 carbon atoms which may be substituted with a fluorine atom. Represents an aryl group having 6 to 12 carbon atoms which may be substituted with a fluorine atom or an aralkyl group having 7 to 12 carbon atoms which may be substituted with a fluorine atom, wherein R ₂ and R ₃ are To form a nitrogen-containing aliphatic ring, and R ₁ and R ₂ may combine to form a cyclic structure.)

  In a non-aqueous electrolyte battery including a negative electrode and a positive electrode, and an electrolyte comprising a non-aqueous solvent and a lithium salt, the electrolyte contains at least one compound represented by the general formula (1), and thus has a high capacity. It has excellent storage characteristics, load characteristics, and cycle characteristics in the case of a secondary battery, and can produce a battery with a small amount of generated gas, and can achieve miniaturization and high performance of a non-aqueous electrolyte battery. it can.

Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of the embodiment of the present invention, and the contents thereof are not specified.
In the present invention, the main components of the non-aqueous electrolytic solution are a lithium salt and a non-aqueous solvent that dissolves the lithium salt, similarly to a commonly used non-aqueous electrolytic solution.
The lithium salt is not particularly limited as long as it is known to be used for this purpose, and any one can be used, and specific examples thereof include the following.

Inorganic lithium salts: Perhalogenates such as LiClO ₄ and fluoride salts such as LiPF ₆ and LiBF ₄ are exemplified. Among them, LiPF ₆ and LiBF ₄ are preferable.
Fluorinated organic acid lithium salt: perfluoroalkane sulfonate such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂₎ perfluoroalkanesulfonic acid imide such _{as, LiC (CF 3 SO 2)} 3 and the like of perfluoroalkane sulfonic acid _{methide, 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 , etc., organic phosphates having a perfluoroalkane group, LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂
And organic borates having a perfluoroalkane group such as LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ . Among them, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and Li
N (C ₂ F ₅ SO ₂ ) ₂ .

These lithium salts may be used alone or in combination of two or more. It is preferable to use an inorganic lithium salt and a fluorine-containing organic lithium salt in combination because deterioration after storage at a high temperature is reduced. In this case, the ratio of the inorganic lithium salt to the lithium salt is desirably 70 to 98% by weight.
When the non-aqueous solvent contains γ-butyrolactone in an amount of 55% by volume or more, the proportion of LiBF _{4 in} the lithium salt is preferably 50% by weight or more. Particularly preferably, the proportion of LiBF _{4 in} the lithium salt is 50 to 95% by weight, with the balance being LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) _2. A combination selected from the group consisting of:

  The concentration of the lithium salt in the non-aqueous electrolyte is usually 0.5 to 3 mol / l. If the concentration is too low, the electric conductivity of the electrolytic solution is insufficient. If the concentration is too high, the electric conductivity decreases due to an increase in viscosity, and the battery performance may decrease. The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.6 mol / l or more, and more preferably 1.8 mol / l or less, particularly preferably 1.5 mol / l or less.

The non-aqueous solvent can also be appropriately selected from those conventionally known as solvents for non-aqueous electrolytes. For example, alkylene carbonates, dialkyl carbonates, cyclic ethers, cyclic carboxylate esters, chain carboxylate esters, organic solvents containing phosphorus and the like can be mentioned.
Examples of the alkylene carbonates include alkylene carbonates having an alkylene group having 2 to 4 carbon atoms, such as ethylene carbonate, propylene carbonate, and butylene carbonate. Of these, ethylene carbonate and propylene carbonate are preferable.

  Examples of the dialkyl carbonates include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, and dialkyl carbonate having an alkyl group having 1 to 4 carbon atoms such as ethyl-n-propyl carbonate. Is mentioned. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferred.

Examples of the cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran.
Examples of chain ethers include dimethoxyethane, dimethoxymethane and the like.
Examples of the cyclic carboxylic acid ester compound include γ-butyrolactone and γ-valerolactone.

Examples of the chain carboxylic acid ester include methyl acetate, methyl propionate, ethyl propionate, and methyl butyrate.
Examples of the phosphorus-containing organic solvent include trimethyl phosphate, triethyl phosphate, dimethylethyl 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 two or more compounds in combination. For example, it is preferable to use a high dielectric constant solvent such as an alkylene carbonate or a cyclic carboxylic acid ester in combination with a low viscosity solvent such as a dialkyl carbonate or a chain carboxylic acid ester.
One of the preferable combinations of the non-aqueous solvent is a combination mainly composed of an alkylene carbonate and a dialkyl carbonate. Among them, the total of the alkylene carbonate and the dialkyl carbonate in the non-aqueous solvent is at least 85% by volume, preferably at least 90% by volume, more preferably at least 95% by volume, and the volume ratio of the alkylene carbonate to the dialkyl carbonate is Is from 10:90 to 45:55, preferably from 20:80 to 45:55. A non-aqueous electrolyte containing a lithium salt and a compound represented by the general formula (1) in the mixed solvent is preferable because the balance between cycle characteristics, large current discharge characteristics, and suppression of gas generation is improved.

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

A combination obtained by further adding propylene carbonate to these combinations of ethylene carbonate and dialkyl carbonate 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 them, those containing ethyl methyl carbonate, which is an asymmetric dialkyl carbonate, are more preferable.Especially, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate and diethyl Those containing ethylene carbonate of carbonate and ethyl methyl carbonate, symmetric dialkyl carbonate and asymmetric dialkyl carbonate are preferable because of good balance between cycle characteristics and large current discharge characteristics.

  Among the non-aqueous solvents, another preferable one is one containing 60% by volume or more of an organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone. A non-aqueous electrolytic solution containing a lithium salt and a compound represented by the general formula (1) in the mixed solvent reduces evaporation and leakage of the solvent even when used at a high temperature. Among them, the sum 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 and propylene carbonate is 30:70 to 70%. 60:40. A non-aqueous electrolytic solution containing a lithium salt and a compound represented by the general formula (1) in the mixed solvent is preferable because the balance between cycle characteristics and large current discharge characteristics is improved.

  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 in an amount of usually 10% by volume or more, preferably 10 to 80% by volume, the flammability of the electrolytic solution can be reduced. In particular, when a phosphorus-containing organic solvent and a non-aqueous solvent selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, and dialkyl carbonate are used in combination, the cycle characteristics and the large current discharge characteristics are improved. This is preferable because the balance is improved.

In addition, in this specification, the capacity of the non-aqueous solvent is a measured value at 25 ° C., but for a solid such as ethylene carbonate at 25 ° C., the measured value at the melting point is used.
In the compound represented by the general formula (1), R _{1 to} R ₃ are each independently an alkyl group having 1 to 12 carbon atoms which may be substituted with a fluorine atom, or may be substituted with a fluorine atom. It represents an alkenyl group having 2 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms which may be substituted by a fluorine atom, or an aralkyl group having 7 to 12 carbon atoms which may be substituted by a fluorine atom.

R ₂ and R ₃ may combine to form a nitrogen-containing aliphatic ring, and examples of the nitrogen-containing aliphatic ring include pyrrolidine and piperidine.
Further, R ₁ and R ₂ may combine to form a cyclic structure, and examples of the cyclic structure include sultams.
Examples of the alkyl group having 1 to 12 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a sec-butyl group, a tert-butyl group, and a pentyl group. No. Of these, an alkyl group having 1 to 8 carbon atoms, particularly 1 to 4 carbon atoms, is preferred.

Examples of the alkenyl group having 2 to 12 carbon atoms include a vinyl group and a propenyl group, and preferably have 2 to 8 carbon atoms, particularly preferably 2 to 4 carbon atoms.
Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a tolyl group, and a xylyl group. Among them, a phenyl group is preferable.
Examples of the aralkyl group having 7 to 12 carbon atoms include a benzyl group and a phenethyl group.

In these alkyl groups, alkenyl groups, aryl groups and aralkyl groups, some or all of the hydrogen atoms may be substituted with fluorine atoms, but those not substituted with fluorine atoms are preferred.
Specific examples of the compound represented by the general formula (1) include N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide, N, N-dipropylmethanesulfonamide, N-methyl-N- Methanesulfonamides such as ethylmethanesulfonamide, N-methyl-N-benzylmethanesulfonamide, 1-methanesulfonylpyrrolidine, 1-methanesulfonylpiperidine, N, N-bistrifluoromethylmethanesulfonamide, N, N-diethyl Ethanesulfonamides such as ethanesulfonamide, N, N-dimethylethanesulfonamide, N-methyl-N-ethylethanesulfonamide; vinylsulfonamides such as N, N-dimethylvinylsulfonamide; N, N-dimethyl Benzenesulfonamide, N, N-diethylbenze Benzenesulfonamides such as sulfonamide, N, N-dipropylbenzenesulfonamide, N, N-dibutylbenzenesulfonamide, N, N-dimethyltrifluoromethanesulfonamide, N, N-bistrifluoromethyltrifluoromethanesulfonamide, etc. Pentafluoroethanesulfonamides such as trifluoromethanesulfonamides, N, N-dimethylpentafluoroethanesulfonamide, N-methylpropanesultam, N-ethylpropanesultam, N-butylpropanesultam, N-methyl Examples include sultams such as butanesultam, N-ethylbutanesultam, and N-propylbutanesultam.

  Of these, methanesulfonamides and ethanesulfonamides are preferable, and since the amount of generated gas is small and the remaining capacity after high-temperature storage is high, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfone are preferable. Amides, N, N-diethylethanesulfonamide and N, N-dimethylethanesulfonamide are particularly preferred. These may be used alone or in combination of two or more.

  The proportion of the compound represented by the general formula (1) in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.05% by weight or more, particularly preferably 0.1% by weight or more. It is at most 5% by weight, preferably at most 4% by weight, particularly preferably at most 3% by weight. If the proportion of the compound of the general formula (1) is too small, gas generation during continuous charging cannot be sufficiently suppressed. On the other hand, if it is too large, the storage characteristics of the battery tend to deteriorate.

Non-aqueous electrolyte solution according to the present invention, as long as the effect of the present invention is not impaired, a cyclic carbonate having an unsaturated bond in the molecule or a conventionally known overcharge inhibitor, a deoxidizing agent, various dehydrating agents such as a dehydrating agent An auxiliary may be contained.
Examples of the cyclic carbonate having an unsaturated bond in the molecule include a vinylene carbonate-based compound, a vinylethylene carbonate-based compound, a methylene ethylene carbonate-based compound, and among these, vinylene carbonate, vinylethylene carbonate, and particularly vinylene carbonate. preferable.

Examples of the vinylene carbonate-based compound include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 4,5-dimethylvinylene carbonate, 4,5-diethylvinylene carbonate, fluorovinylene carbonate, trifluoromethylvinylene carbonate, and the like.
Examples of the vinylethylene carbonate-based compound include vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate, 4-ethyl-4-vinylethylene carbonate, 4-n-propyl-4-vinylethylene carbonate, and 5-methyl-4-carbonate. Examples thereof include vinyl ethylene carbonate, 4,4-divinyl ethylene carbonate, and 4,5-divinyl ethylene carbonate.

Examples of the methylene ethylene carbonate-based compound include 4,4-dimethyl-5-methylene ethylene carbonate and 4,4-diethyl-5-methylene ethylene carbonate.
These may be used alone or in combination of two or more.
When the non-aqueous electrolyte contains a cyclic carbonate compound having an unsaturated bond in the molecule, its proportion in the non-aqueous electrolyte is usually at least 0.01% by weight, preferably at least 0.1% by weight, particularly preferably at least 0.1% by weight. It is preferably at least 0.3% by weight, most preferably at least 0.5% by weight, usually at most 8% by weight, preferably at most 4% by weight, particularly preferably at most 3% by weight.

  By including the cyclic carbonate having an unsaturated bond in the molecule in the electrolytic solution, the cycle characteristics of the battery can be improved. Although the reason is not clear, it is assumed that a stable protective film can be formed on the surface of the negative electrode. If the content is small, this property is not sufficiently improved. In addition, when a cyclic carbonate having an unsaturated bond in the molecule is contained in the electrolytic solution, there is a problem that the amount of generated gas generally increases during continuous charging. However, the compound represented by the general formula (1) When used together, an increase in the amount of gas generation can be suppressed. However, if the content is too high, gas is generated during high-temperature storage, and the internal pressure of the battery may increase. Therefore, the content is preferably within the above range.

In particular, among the compounds represented by the general formula (1), compounds in which some or all of the hydrogen atoms have been replaced by fluorine atoms are easily decomposed by reduction, so that a stable protective film can be formed on the surface of the negative electrode. It is thought that reductive decomposition can be suppressed by using a cyclic carbonate having an unsaturated bond in the molecule in combination.
Examples of the overcharge inhibitor include biphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and aromatic compounds such as dibenzofuran; 2-fluorobiphenyl; Partially fluorinated products of the aromatic compounds such as o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; fluorinated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole and 2,6-difluoroanisole And the like. These may be used in combination of two or more. The proportion of the overcharge inhibitor in the non-aqueous electrolyte is usually 0.1 to 5% by weight. By including an overcharge inhibitor, the battery can be prevented from bursting or firing at the time of overcharge or the like.

In general, these overcharge inhibitors react more easily on the positive electrode and the negative electrode than the solvent component of the electrolytic solution, so that they react at sites with high electrode activity even during continuous charging or high-temperature storage. When the compound reacts, the internal resistance of the battery greatly increases, and gas generation causes the discharge characteristics after continuous charging and the discharge characteristics after high-temperature storage to be remarkably 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 and spiro-bis-dimethylene carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride Carboxylic anhydrides such as acid, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride and phenylsuccinic anhydride; ethylene sulfite, 1,3- Sulfur-containing compounds such as propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone and tetramethylthiuram monosulfide; 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; and heptane, octane, cycloheptane and the like. Examples include hydrocarbon compounds, fluorine-containing aromatic compounds such as fluorobenzene, difluorobenzene, hexafluorobenzene, and benzotrifluoride. These may be used in combination of two or more.

The ratio of these auxiliaries in the non-aqueous electrolyte is usually 0.1 to 5% by weight. By containing these auxiliaries, the capacity retention characteristics after high-temperature storage and the cycle characteristics can be improved.
The non-aqueous electrolyte according to the present invention can be prepared by dissolving a lithium salt, a compound represented by the general formula (1), and other compounds as necessary in a non-aqueous organic solvent. In preparing the non-aqueous electrolyte, each raw material is preferably dehydrated in advance. Usually, it is good to dehydrate to 50 ppm or less, preferably 30 ppm or less.

The nonaqueous electrolyte according to the present invention is suitable for use as an electrolyte for a secondary battery, particularly for a lithium secondary battery. Hereinafter, the lithium secondary battery according to the present invention using the electrolytic solution will be described.
The lithium secondary battery according to the present invention is the same as a conventionally known lithium secondary battery except for the electrolytic solution, and usually, the positive electrode and the negative electrode are provided via a porous membrane impregnated with the nonaqueous electrolytic solution according to the present invention. Stored in the case. Therefore, the shape of the secondary battery according to the present invention is not particularly limited, and may be any of a cylindrical type, a square type, a laminated type, a coin type, a large size, and the like. The lithium secondary battery according to the present invention has a small gas generation amount in the continuous charging state as described above, and therefore, in the continuous charging state of the battery provided with the current interrupting device that operates due to an increase in the battery internal pressure at the time of abnormality such as overcharging. Abnormal operation of the current interrupting device can be prevented. Further, in a battery in which the thickness of the outer package is 0.4 mm or less and the material of the outer package is mainly metal aluminum or an aluminum alloy, a problem of blistering of the battery due to an increase in the internal pressure of the battery is likely to occur. Since the lithium secondary battery generates little gas, it is possible to prevent such a problem from occurring.

As the negative electrode active material, a carbonaceous material or a metal compound capable of inserting and extracting lithium, a lithium metal, and a lithium alloy can be used. These negative electrode active materials may be used alone or in combination of two or more.
As the carbonaceous material capable of occluding and releasing lithium, graphite or a material in which the surface of graphite is coated with amorphous carbon compared to graphite is preferable.

Graphite has a d value (distance between layers) of the lattice plane (002 plane) obtained by X-ray diffraction according to the Gakushin method of 0.3.
It is preferably from 335 to 0.338 nm, particularly preferably from 0.335 to 0.337 nm. The crystallite size (Lc) determined by X-ray diffraction by the Gakushin method is usually at least 30 nm, preferably at least 50 nm, particularly preferably at least 100 nm. 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.

  It is preferable that the surface of graphite is coated with amorphous carbon because graphite having a d value of 0.335 to 0.338 nm on the lattice plane (002 plane) in X-ray diffraction is used as a core material, and A carbonaceous material having a larger d value of the lattice plane (002 plane) in X-ray diffraction than the core material is attached, and the d value of the lattice plane (002 plane) in X-ray diffraction than the core material and the core material Is from 99/1 to 80/20 by weight. By using this, it is possible to produce a negative electrode having a high capacity and hardly reacting with the electrolytic solution.

The particle diameter of the carbonaceous material 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, as a median diameter by a laser diffraction / scattering method. It is more preferably at most 40 μm, most preferably at most 30 μm.
The specific surface area of the carbonaceous material measured by the BET method is usually 0.3 m ² / g or more, preferably 0.5 m ² / g or more.
m ² / g or more, more preferably 0.7 m ² / g or more, and most preferably 0.8 m ² / g or more and usually 25.0 m ² / g or less, preferably 20.0 m ² / g, more It is preferably at most 15.0 m ² / g, most preferably at most 10.0 m ² / g.

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 a simple substance, an oxide, an alloy with lithium, or the like. In the present invention, those containing an element selected from Si, Sn, Ge and Al are preferable, and an oxide or a lithium alloy of a metal selected from Si, Sn and Al is more preferable.
Metal compounds capable of occluding and releasing lithium or their oxides and alloys with lithium have a larger capacity per unit weight than carbon materials typified by graphite, so lithium ions that require higher energy density are required. It is suitable for a secondary battery.

Examples of the positive electrode active material include materials capable of occluding and releasing lithium, such as a lithium transition metal composite oxide material 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, wherein M is at least one selected from Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, V, Sr, and Ti; 4 ≦ x ≦ 1.2 and 0 ≦ y ≦ 0.6.

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 Substitution with a metal is preferable because its structure can be stabilized. The positive electrode active material 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 a solvent or an electrolyte used in manufacturing an electrode. For example, fluorine-based resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyolefins such as polyethylene and polypropylene, styrene-butadiene rubber, isoprene rubber, polymers having unsaturated bonds such as butadiene rubber, and copolymers thereof, ethylene-acrylic An acrylic acid-based polymer such as an acid copolymer and an ethylene-methacrylic acid copolymer, and a copolymer thereof, and the like.

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 carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, 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 production of the electrode may be performed according to a conventional method. For example, it can be formed by adding a binder, a thickener, a conductive material, a solvent, and the like to a negative electrode or a positive electrode active material to form a slurry, applying the slurry to a current collector, drying the current collector, and pressing the same.
In addition, the active material to which a binder or a conductive material is added is roll-formed into a sheet electrode as it is, a pellet electrode is formed by compression molding, or an electrode is formed on a current collector by a method such as vapor deposition, sputtering, or plating. It is also possible to form a thin film of the material.

Drying of the negative electrode active material layer, the density after 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. It is preferable that the density of the negative electrode active material layer be higher since the capacity of the battery increases. The density of the positive electrode active layer after drying and pressing is usually 3.0 g / cm ³ or more. If the density of the positive electrode active layer is too low, the capacity of the battery becomes insufficient.

Various collectors can be used, but usually a metal or an alloy is used. Examples of the current collector for the negative electrode include copper, nickel, and stainless steel, with copper being preferred. Examples of the current collector of the positive electrode include metals such as aluminum, titanium, and tantalum or alloys thereof, and aluminum or alloys thereof are 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 membrane are not particularly limited as long as they are stable in the electrolytic solution and have excellent liquid retention properties, and a porous sheet or a nonwoven fabric made of a polyolefin such as polyethylene or polypropylene is preferable. .

  The material of the exterior body of the battery 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, but the present invention is not limited to these Examples as long as the gist of the present invention is not exceeded.
[Production 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% by weight, the median diameter by laser diffraction / scattering method is 12 μm, and the ratio by BET method The surface area is 7.5 m ² / g, the R value (= I _B / I _A ) determined by Raman spectrum analysis using argon ion laser light is 0.12, and the half width of the peak is in the range of 1570 to 1620 cm ^−1. Was mixed with 94 parts by weight of natural graphite powder having a particle size 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 surface of a copper foil having a thickness of 18 μm, dried, and then pressed so that the density of the negative electrode active layer became 1.5 g / cm ³ to obtain a negative electrode.
[Manufacture of positive electrode]
85 parts by weight of LiCoO ₂ , 6 parts by weight of carbon black and 9 parts by weight of polyvinylidene fluoride (trade name “KF-1000” manufactured by Kureha Chemical Co., Ltd.) were mixed, and N-methyl-2-pyrrolidone was added to form a slurry. After uniformly coating and drying both surfaces of an aluminum foil having a thickness of 20 μm, the aluminum foil was pressed so that the density of the positive electrode active layer became 3.0 g / cm ³ to obtain a positive electrode.
[Manufacture of lithium secondary battery]
The positive electrode, the negative electrode, and the separator made of polyethylene were laminated in this order on the negative electrode, the separator, the positive electrode, the separator, and the negative electrode to prepare a battery element. After inserting the battery element into a bag made of a laminated film in which both surfaces of aluminum (thickness: 40 μm) are covered with a resin layer while projecting the terminals of the positive electrode and the negative electrode, an electrolytic solution to be described later is injected into the bag, and vacuum is applied. Sealing was performed to produce a sheet-shaped battery.
[Capacity evaluation]
A lithium secondary battery was charged to 4.2 V at a constant current corresponding to 0.2 C at 25 ° C. in a state sandwiched between glass plates to enhance adhesion between the electrodes, and then charged at a constant current of 0.2 C. To 3V. After three cycles, the battery is stabilized. In the fourth cycle, the battery is charged at a constant current of 0.5 C to 4.2 V, and then charged at a constant voltage of 4.2 V until the current value becomes 0.05 C. , And 0.2 C at a constant current to 3 V to determine the initial discharge capacity.
[Evaluation of continuous charging characteristics]
After the battery whose capacity evaluation test was completed was immersed in an ethanol bath to measure the volume, the battery was charged at 60 ° C. with a constant current of 0.5 C, and reached a constant voltage of 4.25 V. Switching was performed for one week of continuous charging.

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, the battery was discharged to 3 V at a constant current of 0.2 C at 25 ° C., the remaining capacity after the continuous charge test was measured, and the discharge capacity before the continuous charge test was set to 100 after the continuous charge test. The remaining capacity was determined.
[Evaluation of high-temperature storage characteristics]
The battery after the capacity evaluation test was charged to 4.2 V at a constant current of 0.5 C, charged at a constant voltage of 4.2 V until the current value reached 0.05 C, and then stored at 85 ° C. for 3 days. did. After sufficiently cooling the battery, the battery was discharged at 25 ° C. at a constant current of 0.2 C to 3 V, the remaining capacity after the storage test was measured, and the remaining capacity after storage when the discharge capacity before the storage test was set to 100 was measured. The capacity was determined.
[Evaluation of cycle characteristics]
The battery after the capacity evaluation test was charged at 25 ° C. at a constant current of 0.5 C to 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 0.05 C. A cycle test for discharging to 3V was performed. When the discharge capacity before the cycle test was 100, the discharge capacity after 200 cycles was determined.
(Example 1)
Under a dry argon atmosphere, 1 part by weight of N, N-dimethylmethanesulfonamide was added to 99 parts by weight of a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7), and then sufficiently dried LiPF ₆ was added in an amount of 1.0%. The resulting solution was dissolved in a molar / liter ratio to obtain an electrolytic solution.

Using the obtained electrolyte, a lithium secondary battery was prepared, and its continuous charging characteristics, high-temperature storage characteristics, and cycle characteristics were evaluated. Table 1 shows the evaluation results of the continuous charging characteristics and the high-temperature storage characteristics. Table 2 shows the evaluation results of the cycle characteristics.
(Comparative Example 1)
A lithium secondary battery was prepared using an electrolyte obtained by dissolving sufficiently dry LiPF ₆ in a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7) at a ratio of 1.0 mol / liter. Then, continuous charging characteristics, high-temperature storage characteristics, and cycle characteristics were evaluated. Table 1 shows the evaluation results of the continuous charging characteristics and the high-temperature storage characteristics. Table 2 shows the evaluation results of the cycle characteristics.
(Comparative Example 2)
To 99 parts by weight of a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7), 1 part by weight of 1,1'-sulfonyldiimidazole was added, and then sufficiently dried LiPF ₆ was added at a rate of 1.0 mol / liter. Was dissolved to obtain an electrolyte solution. Using this electrolyte, a lithium secondary battery was prepared, and its continuous charging characteristics and high-temperature storage characteristics were evaluated. The results are shown in Table 1.
(Example 2)
Mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7) to 97 parts by weight, 2 parts by weight of vinylene carbonate, N, N-dimethyl-methanesulfonamide 1 part by weight was added, then LiPF ₆ was thoroughly dried 1 The solution was dissolved at a rate of 0.0 mol / liter to obtain an electrolytic solution.

Using this electrolyte, a lithium secondary battery was prepared, and its continuous charging characteristics, high-temperature storage characteristics, and cycle characteristics were evaluated. Table 1 shows the evaluation results of the continuous charging characteristics and the high-temperature storage characteristics. Table 2 shows the evaluation results of the cycle characteristics.
(Comparative Example 3)
To 98 parts by weight of a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7), 2 parts by weight of vinylene carbonate was added, and then sufficiently dried LiPF ₆ was added to the mixture.
The resulting solution was dissolved at a rate of 0 mol / liter to obtain an electrolytic solution.

Using this electrolyte, a lithium secondary battery was prepared, and its continuous charging characteristics, high-temperature storage characteristics, and cycle characteristics were evaluated. Table 1 shows the evaluation results of the continuous charging characteristics and the high-temperature storage characteristics. Table 2 shows the evaluation results of the cycle characteristics.
(Comparative Example 4)
Mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7) to 97 parts by weight, 2 parts by weight of vinylene carbonate, 1,1 'sulfonyl diimidazole 1 part by weight was added, then LiPF ₆ was thoroughly dried 1 The solution was dissolved at a rate of 0.0 mol / liter to obtain an electrolytic solution.

Using this electrolyte, a lithium secondary battery was prepared, and its continuous charging characteristics and high-temperature storage characteristics were evaluated. The results are shown in Table 1.
(Comparative Example 5)
Mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7) to 97 parts by weight, the addition of vinylene carbonate 2 parts by weight 1 part by weight of 1-p-tolyl sulfonyl pyrrole, then LiPF ₆ was thoroughly dried 1 The solution was dissolved at a rate of 0.0 mol / liter to obtain an electrolytic solution.

Using this electrolyte, a lithium secondary battery was prepared, and its continuous charging characteristics and high-temperature storage characteristics were evaluated. The results are shown in Table 1.
(Example 3)
To 97.5 parts by weight of a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7), 2 parts by weight of vinylene carbonate and 0.5 part by weight of N, N-dimethylmethanesulfonamide were added, and then the mixture was sufficiently dried. LiPF ₆ was dissolved at a ratio of 1.0 mol / liter to prepare an electrolytic solution.

Using this electrolyte, a lithium secondary battery was prepared, and its continuous charging characteristics and high-temperature storage characteristics were evaluated. The results are shown in Table 1.
(Example 4)
Mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7) 97.
To 5 parts by weight, 2 parts by weight of vinylene carbonate and 0.5 parts by weight of N, N-dimethylethanesulfonamide were added, and then sufficiently dried LiPF ₆ was dissolved at a ratio of 1.0 mol / liter. An electrolyte was used.

Using this electrolyte, a lithium secondary battery was prepared, and its continuous charging characteristics and high-temperature storage characteristics were evaluated. The results are shown in Table 1.
(Example 5)
To 97.5 parts by weight of a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7), 2 parts by weight of vinylene carbonate and 0.5 part by weight of N, N-dibutylbenzenesulfonamide were added, and then the mixture was sufficiently dried. LiPF ₆ was dissolved at a ratio of 1.0 mol / liter to prepare an electrolytic solution.

Using this electrolyte, a lithium secondary battery was prepared, and its continuous charging characteristics and high-temperature storage characteristics were evaluated. The results are shown in Table 1.
(Example 6)
To 97.5 parts by weight of a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7), 2 parts by weight of vinylene carbonate and 0.5 part by weight of N, N-diethylmethanesulfonamide were added, and then the mixture was sufficiently dried. LiPF ₆ was dissolved at a ratio of 1.0 mol / liter to prepare an electrolytic solution.

Using this electrolyte, a lithium secondary battery was prepared, and its continuous charging characteristics and high-temperature storage characteristics were evaluated. The results are shown in Table 1.

  As is evident from Tables 1 and 2, the battery according to the present invention generates a small amount of gas even when continuously charged, and has excellent battery characteristics and cycle characteristics after continuous charging and after high-temperature storage. Understand.

Claims (5)

A non-aqueous electrolyte mainly comprising a lithium salt and a non-aqueous solvent dissolving the lithium salt, and further comprising a compound represented by the following general formula (1).

(Wherein, R _{1 to} R ₃ each independently represent an alkyl group having 1 to 12 carbon atoms which may be substituted with a fluorine atom, or an alkenyl having 2 to 12 carbon atoms which may be substituted with a fluorine atom. Represents an aryl group having 6 to 12 carbon atoms which may be substituted with a fluorine atom or an aralkyl group having 7 to 12 carbon atoms which may be substituted with a fluorine atom, wherein R ₂ and R ₃ are To form a nitrogen-containing aliphatic ring, and R ₁ and R ₂ may combine to form a cyclic structure.) The non-aqueous electrolyte according to claim 1, wherein the proportion of the compound represented by the general formula (1) in the non-aqueous electrolyte is 0.01 to 5% by weight. 3. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous electrolyte further contains a cyclic carbonate compound having an unsaturated bond in a ratio of 0.01 to 8% by weight. A lithium secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte according to claim 1. 5. The lithium secondary battery according to claim 4, wherein the negative electrode contains a carbon material having a lattice plane (002) plane having a d value of 0.335 to 0.338 nm in X-ray diffraction.