JP2002359002A - Nonaqueous electrolyte secondary battery and nonaqueous electrolyte used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-energy-density nonaqueous electrolyte secondary battery having a superior cycle characteristics and capacity retaining characteristics at high temperature, and having various types of battery characteristics over a wide temperature range and superior safety such as ignita bility and to provide a nonaqueous electrolyte used therefor. SOLUTION: This nonaqueous electrolyte secondary battery comprises a negative electrode containing, at least, metallic lithium, a lithium alloy, or a material capable of occluding and releasing lithium, a positive electrode containing a material capable of occluding and releasing lithium, and the electrolyte formed by dissolving a lithium salt in a nonaqueous solvent. The nonaqueous solvent is mainly composed of lactone compound and this nonaqueous electrolyte secondary battery contains 0.1-10 wt.% of nitrogen- containing aromatic heterocycle compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte used therefor. In detail, by using a specific non-aqueous electrolyte, it has excellent high-density cycle characteristics and weight retention characteristics at high temperatures, and various battery characteristics over a wide temperature range. The present invention relates to an aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art With the recent reduction in the weight and size of electric products, the development of non-aqueous electrolyte secondary batteries using lithium having a high energy density has been more desired than before.
In addition, with the expansion of application fields of lithium secondary batteries such as electric vehicles, hybrid vehicles, and road leveling, there is a demand for improvements in various battery characteristics.

[0003] Above all, in the problem of waste heat due to miniaturization of electric products, and in automobiles and road leveling used outdoors, the use environment is an environment where the temperature tends to rise, so that the temperature range is higher than before. The improvement of battery performance has become an important issue. At present, a metal oxide salt such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ is used as an active material for the positive electrode, and coke,
Non-aqueous electrolyte secondary batteries using compounds capable of occluding and releasing lithium ions, such as carbonaceous materials such as artificial graphite and natural graphite, and metal oxide materials such as Sn and Si, have been proposed.

At present, these non-aqueous electrolyte secondary batteries have a problem that the cycle characteristics are deteriorated in a high temperature range of 40 ° C. or higher. In order to solve this problem, studies have been made with the aim of improving the cycle characteristics using an electrolyte solution to which an additive has been added, and reports have been made.
Ethylpyridine (Surface Technology Vol. 46, No. 12, 1187, Item 19)
1995), α-picoline, β-picoline and γ-picoline (JP-A-7-105977), quinoxaline,
Nitrogen-containing organic compounds such as indole, 2,3-lutidine, N-methylpyrazole, phenazine, phthalazine, and pyridazine (JP-A-9-204932) are disclosed.

At present, ethylene carbonate is frequently used as a main solvent for the electrolyte of the above-mentioned non-aqueous electrolyte secondary battery because of its high dielectric constant. However, since ethylene carbonate has a high freezing point, is solid at room temperature by itself, and has a high viscosity, an electrolytic solution using ethylene carbonate as a solvent is mixed with a low-viscosity solvent such as dialkyl carbonate such as diethyl carbonate as a secondary solvent. Used as a mixed solvent. However, low-viscosity solvents generally have a low boiling point and a low dielectric constant, so if added in large amounts, the dissociation degree of lithium salts will decrease and the performance of the electrolyte will decrease. On the other hand, there is a problem in terms of safety such as a decrease in point, and conversely, if only a small amount is added, there is a problem in terms of electric conductivity and viscosity at low temperatures.

On the other hand, lactone compounds such as γ-butyrolactone are inferior to ethylene carbonate, but have a sufficiently high dielectric constant, a low freezing point and a low viscosity, so that a sufficient electrolytic solution can be obtained without mixing with a low-viscosity solvent. It is an excellent solvent that can exhibit performance and, as a result, can exhibit performance comparable to an electrolytic solution using a solvent obtained by mixing ethylene carbonate and a low-viscosity solvent.

For this reason, in an electrolyte using γ-butyrolactone as a main solvent, an electrolyte containing about 15 to 35% by volume of ethylene carbonate as a secondary solvent and a non-aqueous electrolyte secondary battery using the same have been proposed. (JP-A-11-31525). However, the electrolytic solution using γ-butyrolactone has a large decrease in cycle characteristics as compared with the electrolytic solution using a solvent in which ethylene carbonate and a low-viscosity solvent are mixed. I was

[0008]

SUMMARY OF THE INVENTION The present invention relates to a non-aqueous electrolyte secondary battery using a lactone compound as a non-aqueous solvent, which has high cycle characteristics at high temperatures and various battery characteristics over a wide temperature range. It is an object of the present invention to provide a high-energy-density nonaqueous electrolyte secondary battery excellent in safety such as ignition performance.

[0009]

The present inventors have made various studies to achieve the above object, and as a result, have found that a non-aqueous electrolyte secondary battery using a non-aqueous solvent mainly composed of a lactone compound. As an electrolytic solution, by using an electrolytic solution containing a nitrogen-containing aromatic heterocyclic compound, compared to a case where the above compound is not used, the cycle characteristics at high temperatures are improved, and the lactone compound is mainly used. The inventors have found that the non-aqueous electrolyte secondary battery using a non-aqueous solvent does not impair the inherent safety of a non-aqueous electrolyte secondary battery, such as low ignitability, and the present invention has been completed.

That is, the gist of the present invention is that at least a negative electrode containing metallic lithium, a lithium alloy or a material capable of inserting and extracting lithium, a positive electrode containing a material capable of inserting and extracting lithium, In a non-aqueous electrolyte secondary battery composed of an electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent, the non-aqueous solvent is a solvent mainly composed of a lactone compound, and a nitrogen-containing aromatic heterocyclic compound In an amount of 0.1 to 10% by weight.

[0011] Another gist of the present invention is to provide a negative electrode including at least metal lithium, a lithium alloy or a material capable of inserting and extracting lithium, and a positive electrode including a material capable of inserting and extracting lithium. An electrolyte for a secondary battery for use in combination, comprising a lithium salt dissolved in a non-aqueous solvent, wherein the non-aqueous solvent is a solvent mainly composed of a lactone compound, and a nitrogen-containing aromatic heterocycle A non-aqueous electrolyte solution containing a compound in an amount of 0.1 to 10% by weight.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. The present invention provides a negative electrode including at least a metal lithium, a lithium alloy or a material capable of occluding and releasing lithium, a positive electrode including a material capable of occluding and releasing lithium, and a lithium salt in a non-aqueous solvent. Wherein the non-aqueous solvent contains a nitrogen-containing aromatic heterocyclic compound, wherein the non-aqueous solvent is a solvent mainly composed of a lactone compound. It is characterized by the following.

The lactone compound solvent has a high degree of dissociation of Li ions, is preferable from the viewpoint of the degree of dissociation of Li, and has a low boiling point and is easily volatilized as seen in a system in which a low viscosity solvent is mixed with ethylene carbonate. In addition, there is no problem in safety such that salt is easily precipitated or volatilized so that flammability is increased at the same time. Therefore, the content of the lactone compound in the non-aqueous solvent is preferably 60% by weight.
Thus, it is preferable to select a combination of non-aqueous solvents that exhibit sufficient battery performance in the range of 70% by weight or more, and most preferably 80% by weight or more.

In the present invention, examples of the lactone compound include γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, δ-caprolactone, ε-caprolactone, and the like. More preferably, the lactone compound in the non-aqueous solvent contains at least 60% by weight of γ-butyrolactone.

The nitrogen-containing aromatic heterocyclic compound used in the present invention is a compound having an aromatic heterocyclic ring containing at least one nitrogen atom in the ring as a part of its structure. In the case of a bicyclic ring, the ring containing a nitrogen atom may be at least one aromatic ring. Further, they may have a substituent as long as the effects of the present invention are not impaired. Specific examples of the nitrogen-containing aromatic heterocyclic compound include the following. (1) Compound having a 6-membered aromatic ring skeleton containing one nitrogen atom (pyridine skeleton) Specifically, for example, pyridine, quinoline, isoquinoline, acridine, phenanthridine, 1,7-phenanthroline, 1,10 Phenanthroline, 4,7-phenanthroline, α-picoline, β-picoline, γ-picoline, 2-acetylpyridine, 3-acetylpyridine,
4-acetylpyridine, 2-phenylpyridine, 3-phenylpyridine, 4-phenylpyridine, 2,6-di-
t-butyl-4-methylpyridine and the like. (2) Compound having a six-membered aromatic ring skeleton containing two nitrogen atoms Specifically, for example, pyridazine, pyrimidine, pyrazine, cinnoline, phthalazine, quinazoline, quinoxaline, 3-methylpyridazine, 4-methylpyridazine,
-Acetylpyridazine, 4-acetylpyridazine, 3-
Phenylpyridazine, 4-phenylpyridazine, 2-methylpyrimidine, 4-methylpyrimidine, 5-methylpyrimidine, 2-acetylpyrimidine, 4-acetylpyrimidine, 5-acetylpyrimidine, 2-phenylpyrimidine, 4-phenylpyrimidine, 5- Phenylpyrimidine, 2-methylpyrazine, 2-acetylpyrazine, 2-
Phenylpyrazine and the like. (3) Compound having a six-membered aromatic ring skeleton containing three or more nitrogen atoms Specifically, for example, 1,2,3-triazine,
2,4-triazine, 1,3,5-triazine, benzotriazine, 4-methyl-1,2,3-triazine, 5
-Methyl-1,2,3-triazine, 4-acetyl-
1,2,3-triazine, 5-acetyl-1,2,3-
Triazine, 4-phenyl-1,2,3-triazine,
5-phenyl-1,2,3-triazine, 1,2,4
5-tetrazine, 3-methyl-1,2,4,5-tetrazine, 3-acetyl-1,2,4,5-tetrazine,
-Phenyl-1,2,4,5-tetrazine and the like. (4) Compound having a five-membered aromatic ring skeleton containing one nitrogen atom (pyrrole skeleton) Specifically, for example, pyrrole, 1-methylpyrrole,
1-vinylpyrrole, 2-methylpyrrole, 3-methylpyrrole, 1-phenylpyrrole, 1-vinylpyrrole, 1-acetylpyrrole, indole, 1-methylindole, 2-methylindole, 3-methylindole, 6-methyl Indole, carbazole, 1-methylcarbazole, oxazole, thiazole, isoxazole, isothiazole, benzoxazole, benzisoxazole, anthranyl, benzothiazole,
1,2-benzoisothiazole, 2,3-benzoisothiazole and the like. (5) Compound having a five-membered aromatic ring skeleton containing two nitrogen atoms Specifically, for example, imidazole, pyrazole, 1,
2,3-oxadiazole, 1,2,3-thiadiazole, 1,2,5-oxadiazole, 1,2,5-thiadiazole, 1,2,4-oxadiazole, 1,2,2
4-thiadiazole, 1,3,4-oxadiazole,
1,3,4-thiadiazole, N-methylimidazole, N-phenylimidazole, N-vinylimidazole, N-acetylimidazole, benzimidazole,
Isoindazole, indazole, benzofurazan and the like. (6) Compound having a five-membered aromatic ring skeleton containing three or more nitrogen atoms Specifically, for example, 1H-1,2,3-triazole, 2H-1,2,3-triazole, 1H-1, 2,
4-triazole, 4H-1,2,4-triazole,
1,2,3,4-oxatriazole, 1,2,4,5
-Oxatriazole, 1,2,3,4-thiatriazole, 1,2,4,5-thiatriazole, 1-benzotriazole, 2-benzotriazole, 2H-1,
2,3,4-tetrazole, 1-methyl-1H-1,
2,3-triazole, 1-vinyl-1H-1,2,3
-Triazole, 1-acetyl-1H-1,2,3-triazole, 1-phenyl-1H-1,2,3-triazole and the like.

These nitrogen-containing aromatic heterocyclic compounds are
More than one kind may be mixed and used, or a mixture that is difficult to separate may be used without separation. Further, their content in the non-aqueous solvent is 0.01 to 10% by weight, and 0.05 to 8% by weight.
% By weight, more preferably 0.1 to 5% by weight.
If the amount is too small, a sufficient film cannot be formed, and if the amount is too large, excess film formation may adversely affect battery characteristics.

Further, various additives such as a conventionally known film forming agent, an overcharge preventing agent, a dehydrating agent and a deoxidizing agent may be mixed and used in the electrolytic solution of the present invention. For example, conventionally known film forming agents, unsaturated cyclic carbonates such as vinylene carbonate, cyclic sulfides such as ethylene sulfide, cyclic saturated carbonates having an unsaturated hydrocarbon group such as vinyl ethylene carbonate, cyclic sultone such as propane sultone, Phenyl ethylene carbonate and at least one compound selected from the group consisting of cyclic carboxylic acid anhydrides such as succinic anhydride, malonic anhydride, maleic anhydride, and phthalic anhydride are used in an electrolyte solution in an amount of 0.1 to 1%.
When the content is 0% by weight, preferably 0.1 to 8% by weight, the capacity retention characteristics and the cycle characteristics are good.

As a solute of the electrolytic solution used in the present invention, a lithium salt is used. For lithium salts,
There is no particular limitation as long as it can be used as a solute of the electrolytic solution. Specific examples thereof include the following. (1) Inorganic lithium salt: LiPF ₆ , LiAsF ₆ , Li
_{BF 4, LiTaF 6, LiAlF 4} , LiAlF 6, Li
Inorganic fluoride salts such as SiF _{6, and} perhalogen salts such as LiClO ₄ . (2) Organic lithium salts: organic sulfonates such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO)
₂ ) ₂ , a perfluoroalkylsulfonic acid imide salt such as LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃
Perfluoroalkylsulfonic acid methide salts such as SO ₂ ) ₃ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) ₃ , L
iBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₃
A salt in which some fluorine atoms of an inorganic fluoride salt such as (CF ₃ ) are substituted with a perfluoroalkyl group, LiB (CF ₃ C
OO) ₄ , LiB (OCOCF ₂ COO) ₂ , LiB (O
Lithium tetrakis (perfluorocarboxylate) borate salts such as COC ₂ F ₄ COO) ₂ .

These solutes may be used as a mixture of two or more kinds. Among these, from the viewpoints of solubility, ionic dissociation degree and electric conductivity characteristics, LiPF ₆ , LiBF ₄ ,
LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , L
iN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiPF ₃ (CF
₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiBF ₂ (C ₂ F ₅ ) ₂ and LiB (OCOCF ₂ COO) ₂ are more preferable;
PF ₆ and LiBF ₄ are more preferred. In particular, the dielectric constant 2
When a non-aqueous solvent containing 60% by weight or more of γ-butyrolactone is selected as 5 or more non-aqueous solvents, LiBF ₄ is preferably 50% by weight or more of the whole lithium salt.

The concentration of the solute lithium salt in the electrolytic solution of the present invention is desirably 0.5 to 3 mol / l. If the concentration is too low, the electric conductivity of the electrolytic solution becomes insufficient due to the absolute lack of concentration, and if the concentration is too high, the electric conductivity decreases due to an increase in viscosity, and precipitation at low temperatures tends to occur. Therefore, the performance of the battery is lowered, which is not preferable.

The material of the negative electrode constituting the secondary battery of the present invention is not particularly limited as long as it contains a material capable of inserting and extracting lithium. Specific examples thereof include, for example, various thermal decomposition conditions. Thermal decomposition products of organic substances, carbonaceous materials such as artificial graphite and natural graphite, metal oxide materials, lithium metal and various lithium alloys. Of these, preferred as carbonaceous materials are artificial graphite and purified natural graphite produced by high-temperature heat treatment of graphitic pitch obtained from various raw materials, or materials obtained by subjecting these graphites to various surface treatments including pitch. It is.

These graphite materials usually have a d value (interlayer distance) of the lattice plane (002 plane) determined by X-ray diffraction according to the Gakushin method of 0.335 to 0.34 nm, more preferably 0.3 to 0.34 nm.
Those having a thickness of 35 to 0.337 nm are preferred. These graphite materials usually have an ash content of 1% by weight or less, more preferably 0.5% by weight or less, and most preferably 0.1% by weight or less, and a crystallite size (X-ray diffraction obtained by Gakushin method). Lc) is preferably 30 nm or more. Further, the crystallite size (Lc) is more preferably 50 nm or more, and most preferably 100 nm or more.

The median diameter of the graphite material is a median diameter determined by a laser diffraction / scattering method and is usually 1 to 100 μm.
m, preferably 3 to 50 μm, more preferably 5 to 40
μm, and more preferably 7 to 30 μm. The BET specific surface area of the graphite material is usually from 0.5 to 25.0 m ² / g.
And preferably 0.7 to 20.0 m ² / g, more preferably 1.0 to 15.0 m ² / g, and still more preferably 1.5 to 10.0 m ² / g. In Raman spectrum analysis using argon ion laser light, 1
Peak P _A (peak intensity I _A) in the range of 580～1620Cm ^-1 and the peak P _B (peak intensity I _B) in the range of 1350 ^-1 of the intensity ratio R = I _B / I _A is typically 0
The half-value width of the peak in the range of ～0.5,1580～1620Cm ^-1 is 26cm ^-1 or less, and more preferably preferably 25 cm ^-1 or less.

Further, these carbonaceous materials may be mixed with other negative electrode materials capable of inserting and extracting lithium. As the negative electrode material capable of inserting and extracting lithium other than the carbonaceous material, Ag, Zn, Al, Ga, In, Si,
Ge, Sn, Pb, P, Sb, Bi, Cu, Ni, S
Metal oxide materials such as alloys of metals such as r and Ba with Li, or oxides of these metals, and lithium metals are preferable, but Sn oxide, Si oxide, Al oxide, Sn, Si , Al lithium alloys and metallic lithium.

These negative electrode materials may be used as a mixture of two or more kinds. The method for producing a negative electrode using these negative electrode materials is not particularly limited. For example, a negative electrode can be manufactured by adding a binder, a thickener, a conductive material, a solvent, and the like to a negative electrode material as needed to form a slurry, applying the slurry to a current collector substrate, and drying. Alternatively, the negative electrode material can be roll-formed as it is to form a sheet electrode, or can be formed into a pellet electrode by compression molding.

When a binder is used in the production of an electrode, there is no particular limitation as long as the material is stable with respect to the solvent and electrolyte used in the production of the electrode and other materials used in the use of the battery. Specific examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber,
Examples include isoprene rubber and butadiene rubber.

When a thickener is used in the production of the electrode, there is no particular limitation as long as it is a material that is stable with respect to the solvent and electrolyte used in the production of the electrode and other materials used in the use of the battery. Specific examples thereof include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose,
Ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and the like can be mentioned.

When a conductive material is used for manufacturing an electrode, there is no particular limitation as long as the material is stable with respect to a solvent and an electrolyte used in manufacturing the electrode and other materials used in using a battery. Specific examples include metal materials such as copper and nickel,
Carbon materials such as graphite, carbon black and the like can be mentioned. As the material of the current collector for the negative electrode, metals such as copper, nickel, and stainless steel are used, and among these, copper foil is preferable from the viewpoint of easy processing into a thin film and cost.

As the material of the positive electrode constituting the secondary battery of the present invention, a lithium transition metal composite oxide material such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide or the like can absorb and release lithium. Materials can be used. The method for manufacturing the positive electrode is not particularly limited, and the positive electrode can be manufactured according to the above-described method for manufacturing the negative electrode. As for the shape, a binder, a conductive material, a solvent, etc. are added to the positive electrode material as necessary and mixed,
A sheet electrode can be formed by applying the composition to a current collector substrate, or a pellet electrode can be formed by press molding.

As the material of the current collector for the positive electrode, a metal such as aluminum, titanium, and tantalum or an alloy thereof is used.
Among them, aluminum or its alloy is particularly preferable in terms of energy density because of its light weight. Regarding the material and shape of the separator used in the secondary battery of the present invention,
There is no particular limitation. However, it is preferable to select from materials that are stable to the electrolytic solution and have excellent liquid retention properties, and it is preferable to use a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene as a raw material.

The method for producing the secondary battery of the present invention comprising at least the negative electrode, the positive electrode, and the non-aqueous electrolyte is not particularly limited, and can be appropriately selected from commonly employed methods. The shape of the battery is not particularly limited, and a cylinder type in which a sheet electrode and a separator are formed into a spiral shape, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, and a coin type in which a pellet electrode and a separator are stacked are used. It is possible.

[0032]

The present invention will now be described with reference to Examples and Comparative Examples.
Specific embodiments will be further described.
Unless limited by these examples.
Not. Example 1 2,6-Di-tert-butyl-4-meth was added to γ-butyrolactone.
Dissolve 5% by weight of tylpyridine and dry
Lithium borofluoride thoroughly dried under gon atmosphere
(LiBF_Four) At a rate of 1 mol / liter
Prepare electrolyte solution and make coin cell by the method described below
And repeat the charge / discharge test at 60 ° C for one cycle.
Discharge capacity at the 100th cycle against the discharge capacity at the 100th cycle
Was determined. The results are shown in Table 1. Example 2 Quinoline is dissolved in γ-butyrolactone at a ratio of 5% by weight.
And LiBF_FourDissolved at a rate of 1 mol / liter
As in Example 1 except that the electrolyte solution prepared in
And evaluated. The results are shown in Table 1. Example 3 α-picoline was added to γ-butyrolactone at a ratio of 5% by weight.
Dissolves and further LiBF _FourAt a rate of 1 mol / l
Same as Example 1 except that the electrolytic solution prepared by
Evaluation was performed as described above. The results are shown in Table 1. Example 4 Pyridazine was dissolved in γ-butyrolactone at a ratio of 5% by weight.
Understand, then LiBF_FourDissolved at a rate of 1 mol / l
Same as Example 1 except that the prepared electrolyte was used.
Was evaluated. The results are shown in Table 1. Example 5 1,2,3-Triazine was added to γ-butyrolactone in an amount of 5% by weight.
% And further dissolved in LiBF_Four1 mol / liter
Except that an electrolyte prepared by dissolving at a
Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
You. Example 6 1-methylpyrrole was added to γ-butyrolactone in an amount of 5% by weight.
Dissolved in a proportion_FourOf 1 mol / liter
Example except that the electrolyte solution prepared by dissolution was used.
Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1. Example 7 Pyridine is dissolved in γ-butyrolactone at a ratio of 5% by weight.
And then dissolve vinylene carbonate at a ratio of 5% by weight.
And then LiBF_FourAt a rate of 1 mol / l
Same as Example 1 except that the electrolytic solution prepared by
Evaluation was performed as described above. The results are shown in Table 1. Comparative Example 1 LiBF was used without adding other additives to γ-butyrolactone.
_FourElectrolyte prepared by dissolving 1 mol / liter
Evaluation was performed in the same manner as in Example 1 except that
Was. The results are shown in Table 1. Comparative Example 2 5% by weight of vinylene carbonate to γ-butyrolactone
Dissolved in the ratio of_FourOf 1 mol / liter
Implemented except using electrolyte solution prepared by dissolving in proportion
Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
You. Comparative Example 3 LiPF was added to propylene carbonate.₆1 mol / l
Other than using an electrolyte solution prepared by dissolving at
Was evaluated in the same manner as in Example 1. Table 1 shows the results.
Shown in

[0033]

[Table 1] Evaluation of Secondary Battery The evaluation of the electrolytic solution and the secondary battery in Examples was performed as follows. [Preparation of Positive Electrode] As a positive electrode active material, 85% by weight of LiCoO _2, 6% by weight of carbon black and 9% by weight of polyvinylidene fluoride (KF-1000, trade name, KF-1000) were added and mixed, and mixed with N-methylpyrrolidone. The dispersion and the slurry were uniformly coated on a 20 μm-thick aluminum foil serving as a positive electrode current collector, dried, and then dried to a diameter of 12.5 m.
m to form a positive electrode. [Preparation of Negative Electrode] The d value of the lattice plane (002 plane) in X-ray diffraction was 0.336 nm, and the crystallite size (Lc) was 100.
nm or more (264 nm), ash content: 0.04% by weight, median diameter by laser diffraction / scattering method: 17 μm, BET
Has a specific surface area of 8.9 m ² / g and a Raman spectrum analysis using argon ion laser light of 1580 to 1
Intensity ratio R = I _B / I _A of the peak P _A in the range of 620 cm ^-1 (peak intensity I _A) and peak in the range of 1350 ^-1 P _B (peak intensity I _B) is 0.15,158
The half width of the peak in the range of ⁰ to 1620 cm ^-1 is 22.2.
cm ^-1 artificial graphite powder (manufactured by Timcal, trade name KS
-44) Styrene dispersed in distilled water at 94% by weight
Butadiene rubber (SBR) was added to a solid content of 6% by weight, mixed with a disperser, and a slurry was uniformly applied on a 18 μm-thick copper foil as a negative electrode current collector, and dried. Thereafter, the resultant was punched into a disk having a diameter of 12.5 mm to produce an electrode, which was used as a negative electrode. [Preparation of coin-type cell] Using a positive electrode, a negative electrode, and an electrolytic solution, a positive electrode is housed in a stainless steel can that also serves as a positive electrode conductor, and is passed through a polyethylene separator impregnated with an electrolytic solution thereon. The negative electrode was mounted. The can body and the sealing plate also serving as the negative electrode conductor were caulked and sealed via an insulating gasket to produce a coin cell. [Evaluation of Coin Cell] At 25 ° C., a charge / discharge test was performed at a constant current of 0.5 mA at a charge end voltage of 4.2 V and a discharge end voltage of 3.0 V, and a charge / discharge test of 100 cycles was performed. At this time, a value obtained by dividing the discharge capacity at the 100th cycle by the discharge capacity at the first cycle was defined as the ratio of the discharge capacity.

[0034]

According to the present invention, the cycle characteristics at high temperatures are improved, and the safety of the non-aqueous electrolyte secondary battery using a non-aqueous solvent mainly composed of a lactone compound, which is inherently low in ignition properties and the like, is obtained. A non-aqueous electrolyte secondary battery with higher performance can be provided without loss.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Shinichi Kinoshita, Inventor Shinichi Kinoshita 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Prefecture Mitsubishi Chemical Corporation (72) Inventor Makoto Ue 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki No. 1 Mitsubishi Chemical Corporation F-term (reference)

Claims (9)

[Claims] 1. A negative electrode containing at least metal lithium, a lithium alloy or a material capable of inserting and extracting lithium, a positive electrode containing a material capable of inserting and extracting lithium, and a lithium salt in a non-aqueous solvent. And a non-aqueous electrolyte secondary battery composed of an electrolytic solution obtained by dissolving the compound, wherein the non-aqueous solvent is a solvent mainly containing a lactone compound, and the nitrogen-containing aromatic heterocyclic compound is 0.1 to 10%. A non-aqueous electrolyte secondary battery, characterized in that it contains about 10% by weight. 2. The non-aqueous system according to claim 1, wherein the nitrogen-containing aromatic heterocyclic compound is at least one compound selected from the group consisting of a pyridine skeleton, a pyrrole skeleton, an imidazole skeleton, and a compound having a pyrimidine skeleton. Electrolyte secondary battery. 3. The nitrogen-containing aromatic heterocyclic compound is at least one compound selected from the group consisting of pyridine, pyrrole, 1-methylpyrrole, quinoline, isoquinoline, 1-methylimidazole and pyrimidine. 3. The non-aqueous electrolyte secondary battery according to 2. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lactone compound contains γ-butyrolactone. 5. An electrolytic solution comprising 0.1 to 10% by weight of at least one compound selected from the group consisting of vinylene carbonate, ethylene sulfide, vinyl ethylene carbonate, propane sultone, phenyl ethylene carbonate and cyclic carboxylic anhydride. %.
5. The non-aqueous electrolyte secondary battery according to any one of items 1 to 4. 6. The method according to claim 1, wherein the lithium salt is LiPF _{6 or} LiBF.
₄ or at least one inorganic lithium salt selected from LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C
F ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO
₂ ), LiPF ₃ (C ₂ F ₅ ) ₃ and LiB (CF ₃ COO)
The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is at least one kind of organic lithium salt selected from the group consisting of ₄ . 7. The lactone compound contains 50% by weight or more of γ-butyrolactone, and contains vinylene carbonate, ethylene sulfide, vinyl ethylene carbonate, propane sultone, phenyl ethylene carbonate, succinic anhydride, malonic anhydride, 0.1 to 10% by weight of at least one compound selected from the group consisting of maleic anhydride and phthalic anhydride;
BF is a _4, a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6. 8. A negative electrode material capable of inserting and extracting lithium has a lattice plane (002 plane) having a d-value of 0.1 in X-ray diffraction.
335-0.34 nm carbonaceous material and / or S
at least one selected from the group consisting of n, Si and Al
The non-aqueous electrolyte secondary battery according to claim 1, comprising a metal oxide and / or a lithium alloy. 9. A method for use in combination with at least a negative electrode including metallic lithium, a lithium alloy or a material capable of inserting and extracting lithium, and a positive electrode including a material capable of inserting and extracting lithium. An electrolyte for a secondary battery, comprising a lithium salt dissolved in a non-aqueous solvent, wherein the non-aqueous solvent is a solvent mainly composed of a lactone compound, and the nitrogen-containing aromatic heterocyclic compound is 0.1 to 0.1%. 1
A non-aqueous electrolyte solution containing 0% by weight.