JP5326846B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to a non-aqueous liquid electrolyte secondary battery that ensures safety during overcharging and has high capacity and excellent storage characteristics, load characteristics, and cycle characteristics.

  In recent years, as electronic devices have been reduced in size and weight, a nonaqueous system using a negative electrode capable of inserting and extracting lithium, a positive electrode, and an electrolytic solution obtained by dissolving a lithium salt in a nonaqueous solvent Electrolyte secondary batteries have high voltage and high energy density, and are excellent in storability, so they are widely used as power sources for consumer electronic devices such as handy video cameras and portable personal computers. Yes. Non-aqueous electrolyte secondary batteries that perform battery functions by occluding and releasing lithium ions are called lithium ion secondary batteries, and their development and commercialization competition are intensifying. Furthermore, due to environmental problems, attention has been focused on large capacity, high energy density and sealed maintenance-free lithium ion secondary batteries for electric vehicles and power load leveling.

Since the capacity per weight is large in the positive electrode active material of a lithium ion secondary battery, lithium transition metal composite oxides such as layered lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) are mainly used. Although they are used, they have significant problems. This is because these lithium transition metal composite oxides become extremely unstable in an overcharged state (a state in which lithium ions are almost eliminated), causing a rapid exothermic reaction with the electrolyte, or depositing lithium metal on the negative electrode. In the worst case, the battery will burst or ignite.

  In order to solve such problems, for example, Japanese Patent Laid-Open No. 9-106835 discloses that an internal resistance of a battery is increased by mixing an additive that polymerizes at a battery voltage equal to or higher than the maximum operating voltage of the battery in an electrolyte. In order to protect the battery, Japanese Patent Application Laid-Open No. 9-171840 discloses an additive that generates gas and pressure by polymerizing at a battery voltage higher than the maximum operating voltage of the battery in the electrolyte. By mixing, it has been proposed to reliably operate an internal electrical disconnection device provided for overcharge protection, and aromatic compounds such as biphenyl, thiophene, and furan are disclosed as additives.

  Furthermore, various aromatic compounds have been proposed to improve safety during overcharge. However, when these compounds are added, there is an effect on safety at the time of overcharge, but there is a problem that the discharge characteristics of the battery under normal use, particularly the discharge characteristics after high temperature storage are remarkably deteriorated. In order to solve such a problem, Japanese Patent Application Laid-Open No. 2001-126765 discloses electrolysis as a battery capable of suppressing a decrease in recovery capacity after high-temperature storage while suppressing rupture damage of the battery during overcharge. It has been proposed to include biphenyl and propane sultone in the liquid, and some effects are seen, but the load characteristics and cycle characteristics are not sufficient.

  The present invention has been made in view of the above problems, and provides a non-aqueous liquid electrolyte secondary battery having high capacity and excellent storage characteristics, load characteristics and cycle characteristics while ensuring safety during overcharge. The issue is to provide.

  As a result of intensive studies in order to achieve the above-mentioned problems, the present inventor can secure safety during overcharge and improve storage characteristics and cycle characteristics by using an electrolytic solution having a specific composition. I found what I could do and came to complete this invention.

  That is, the gist of the present invention is a non-aqueous electrolyte secondary battery comprising at least a negative electrode capable of inserting and extracting lithium, a positive electrode, and an electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent. A compound that reacts at a voltage higher than the maximum operating voltage of the battery when overcharged in the non-aqueous solvent, at least one compound selected from the group consisting of a cyclic carbonate having an unsaturated bond and an acid anhydride, and a sulfur-containing compound. The present invention resides in a non-aqueous electrolyte secondary battery comprising an organic compound.

  Another gist of the present invention is a non-aqueous electrolyte solution for a non-aqueous electrolyte secondary battery comprising at least a negative electrode capable of inserting and extracting lithium and a positive electrode, wherein the non-aqueous electrolyte solution is a non-aqueous electrolyte solution. A compound composed of at least a non-aqueous solvent and a lithium salt, and reacts with the non-aqueous solvent at a voltage equal to or higher than the maximum operating voltage of the battery when overcharged, a cyclic carbonate having an unsaturated bond, and an acid anhydride. The present invention resides in a nonaqueous electrolytic solution for a secondary battery comprising at least one selected compound and a sulfur-containing organic compound.

  The reason for the improvement of the storage characteristics by using the electrolytic solution is not sufficiently clear. Conventionally, a compound (overcharge inhibitor) that reacts at a voltage higher than the maximum operating voltage of the battery during overcharge is more likely to react on the positive electrode and the negative electrode than the solvent component of the electrolyte solution. When these compounds react with each other at a site having high activity, the internal resistance of the battery is greatly increased, and due to gas generation, the discharge characteristics after high-temperature storage are significantly reduced. In the present invention, an electrolytic solution containing at least one compound selected from the group consisting of a cyclic carbonate having an unsaturated bond and an acid anhydride and a sulfur-containing organic compound is used. The cyclic ester carbonate or acid anhydride having a bond efficiently forms a film of a reduction reaction product derived from the initial charge on the negative electrode surface, and this film is stable even in a high temperature environment. Suppresses the reaction between the charge inhibitor and the negative electrode, and the sulfur-containing organic compound suppresses the reactivity of the positive electrode by adsorption or reaction to the active site of the positive electrode, thereby causing the reaction between the overcharge inhibitor and the positive electrode. By suppressing it, it is thought that the remarkable fall of the discharge characteristic after high temperature storage is suppressed.

  By using the non-aqueous electrolyte of the present invention, it is possible to ensure a safety during overcharge and to produce a battery with high capacity and excellent storage characteristics, load characteristics and cycle characteristics. This can contribute to downsizing and higher performance of the secondary battery.

  Hereinafter, embodiments of the present invention will be described in detail. The non-aqueous electrolyte for a secondary battery of the present invention is composed of at least a non-aqueous solvent and a lithium salt, and a compound that reacts with the non-aqueous solvent at a voltage higher than the maximum operating voltage of the battery when overcharged, and an unsaturated bond It contains at least one compound selected from the group consisting of cyclic carbonates having acid and acid anhydrides, and sulfur-containing organic compounds.

  The nonaqueous solvent used in the present invention contains a compound (overcharge inhibitor) that reacts at a voltage higher than the maximum operating voltage of the battery during overcharge. The compound (overcharge inhibitor) that reacts at a voltage higher than the maximum operating voltage of the battery at the time of overcharge is not particularly limited. However, when a lithium-containing transition metal oxide is used as the positive electrode active material, the compound reacts in the normal operating potential range. However, a substance that reacts at around 4.5 V is preferable, and an aromatic compound is mainly used. Specific examples of the overcharge inhibitor include biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, diphenyl ether, benzofuran, dibenzofuran, and halides such as 2-fluorobiphenyl, mainly fluorine. And fluorine-containing anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, and 2,6-difluoroanisole. These compounds may be used in combination of two or more.

  The content of the overcharge inhibitor in the non-aqueous solvent is not particularly limited, but is preferably 0.01 to 5% by weight, more preferably 0.1 to 4% by weight. The non-aqueous solvent used in the present invention contains a compound selected from a cyclic carbonate having an unsaturated bond or an acid anhydride. The cyclic ester carbonate having an unsaturated bond is not particularly limited. For example, vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, fluorovinylene carbonate, trifluoromethyl. Vinylene carbonate compounds such as vinylene carbonate, 4-vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate, 4-ethyl-4-vinylethylene carbonate, 4-n-propyl-4-vinylethylene carbonate, 5-methyl- 4-vinylethylene carbonate, 4,4-divinylethylene carbonate, 4,5-divinylethylene carbonate, 4,4-dimethyl-5-methyleneethylene carbonate, 4,4- Ethyl-5-methylene ethylene carbonate. Among these, vinylene carbonate, 4-vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate, and 4,5-divinylethylene carbonate are preferable, and vinylene carbonate and 4-vinylethylene carbonate are more preferable.

  The acid anhydride is not particularly limited, and may be a compound having a plurality of acid anhydride structures in one molecule. Specific examples of the acid anhydride include acetic anhydride, propionic anhydride, butyric anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexane. Dicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic An acid anhydride, phenyl succinic anhydride, 2-phenyl glutaric anhydride, phthalic anhydride, pyromellitic anhydride, etc. can be mentioned. Of these, succinic anhydride, glutaric anhydride, and cyclohexanedicarboxylic anhydride are preferable.

  Two or more cyclic carbonates or acid anhydrides having an unsaturated bond may be used in combination. The content of the compound selected from the cyclic carbonate having an unsaturated bond or the acid anhydride in the non-aqueous solvent is not particularly limited, but is preferably 0.01 to 5% by weight, more preferably 0.1 to 5% by weight. It is. In particular, in the case of a cyclic carbonate having an unsaturated bond, it is preferably 0.1 to 4% by weight, and in the case of an acid anhydride, it is preferably 0.1 to 3% by weight.

  Moreover, the non-aqueous solvent used in the present invention contains a sulfur-containing organic compound. The sulfur-containing organic compound is not particularly limited, for example, ethylene sulfite, propylene sulfite, butylene sulfite, vinylene sulfite, cyclic sulfite such as tetrahydrofuran sulfite, dimethyl sulfite, diethyl sulfite, ethyl methyl sulfite, Chain sulfites such as methyl propyl sulfite and ethyl propyl sulfite, halides of the above cyclic sulfites and chain sulfites, sulfolane, 2-methyl sulfolane, 3-methyl sulfolane, 2-ethyl sulfolane, 3-ethyl sulfolane , 2,4-dimethylsulfolane, sulfolene, cyclic sulfones such as 2-methylsulfolene, 3-methylsulfolene, dimethylsulfone, diethylsulfone, ethylmethylsulfone, methylpropylsulfone Chain sulfones such as ethylpropyl sulfone, divinyl sulfone, methyl vinyl sulfone, diphenyl sulfone, dibenzyl sulfone, halides of the above cyclic sulfones and chain sulfones, 1,3-propane sultone, 1,4-butane sultone, 2, Cyclic sulfonic acid esters such as 4-butane sultone, 1,3-butane sultone, 3-phenyl-1,3-propane sultone, 4-phenyl-1,4-butane sultone, methyl methanesulfonate, ethyl methanesulfonate, methanesulfonic acid Propyl, methyl ethane sulfonate, ethyl ethane sulfonate, propyl ethane sulfonate, methyl benzene sulfonate, ethyl benzene sulfonate, propyl benzene sulfonate, phenyl methane sulfonate, phenyl ethane sulfonate, propane sulfo Chain sulfonates such as phenyl acid, methyl benzyl sulfonate, ethyl benzyl sulfonate, propyl benzyl sulfonate, benzyl methanesulfonate, benzyl ethanesulfonate, benzyl propanesulfonate, busulfan, etc. Sulfonate halides, ethylene glycol sulfate, 1,2-propanediol sulfate, 1,3-propanediol sulfate, 1,2-butanediol sulfate, 1,3-butanediol sulfate, 2, Cyclic sulfates such as 3-butanediol sulfate, phenylethylene glycol sulfate, dimethyl sulfate, diethyl sulfate, ethyl methyl sulfate, methyl propyl sulfate, ethyl propyl sulfate, methyl phenyl sulfate, sulfuric acid ester Examples thereof include chain sulfates such as tilphenyl, phenylpropyl sulfate, benzylmethyl sulfate, and benzylethyl sulfate, halides of the above cyclic sulfates and chain sulfates, etc. Among them, ethylene sulfite, 1,3-propane Sultone, dimethyl sulfone, and methyl methanesulfonate are preferred. These sulfur-containing organic compounds may be used as a mixture of two or more.

  The content of the sulfur-containing organic compound in the non-aqueous solvent is not particularly limited, but is preferably 0.01 to 5% by weight, more preferably 0.1 to 5% by weight, still more preferably 0.1 to 3% by weight. is there. Furthermore, in the present invention, when a non-aqueous solvent contains a fluorine-containing aromatic compound having 9 or less carbon atoms, an aliphatic hydrocarbon, or a fluorine-containing aliphatic hydrocarbon compound, a large current discharge after high-temperature storage Characteristics can be improved.

  The fluorine-containing aromatic compound having 9 or less carbon atoms is not particularly limited. For example, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluoro Benzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene, 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2, 4,5-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, 2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluoro Toluene, 2,6-difluorotoluene, 3,4-difluorotoluene, benzotrifluoride, -Fluorobenzotrifluoride, 3-fluorobenzotrifluoride, 4-fluorobenzotrifluoride, 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2-fluoro-m-xylene, 5-fluoro-m- Examples include xylene, 2-methylbenzotrifluoride, 3-methylbenzotrifluoride, 4-methylbenzotrifluoride, octafluorotoluene and the like.

  The aliphatic hydrocarbon is not particularly limited. For example, hexane, heptane, octane, nonane, decane, 2-methylhexane, 3-methylhexane, 2-methylheptane, 3-methylheptane, cyclohexane, cycloheptane. , Cyclooctane, methylcyclohexane, ethylcyclohexane, butylcyclohexane, dicyclohexyl, decalin and the like.

  Examples of the fluorine-containing aliphatic hydrocarbon compound include fluorinated products of the aliphatic hydrocarbons such as 1-fluorohexane and 1-fluoroheptane. Among the compounds selected from the fluorine-containing aromatic compounds, aliphatic hydrocarbons or fluorine-containing aliphatic hydrocarbon compounds having 9 or less carbon atoms, fluorobenzene, benzotrifluoride and heptane are preferable. These compounds may be used as a mixture of two or more.

  Although content of these compounds in a nonaqueous solvent is not specifically limited, Preferably it is 0.1 to 10 weight%, More preferably, it is 0.2 to 5 weight%. When a fluorine-containing aromatic compound having 9 or less carbon atoms, an aliphatic hydrocarbon, or a fluorine-containing aliphatic hydrocarbon compound is contained in a non-aqueous solvent, these compounds are relatively stable against oxidation and reduction. By being present on the surfaces of the positive electrode and the negative electrode, it is considered that the opportunity for the overcharge inhibitor to react on the surfaces of the positive electrode and the negative electrode can be reduced, and as a result, the high current discharge characteristics after high-temperature storage can be improved. The non-aqueous solvent used in the present invention is not particularly limited, and examples thereof include cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate, dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, and ethyl methyl carbonate. (Preferably one having 1 to 4 carbon atoms in the alkyl group), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, chain ethers such as dimethoxyethane and dimethoxymethane, cyclic esters such as γ-butyrolactone and γ-valerolactone And chain esters such as methyl acetate, methyl propionate and ethyl propionate, and phosphorus-containing organic solvents such as trimethyl phosphate and triethyl phosphate. Two or more kinds of these solvents may be mixed and used.

  The non-aqueous solvent contains 20% by volume or more of alkylene carbonate having 2 to 4 carbon atoms in the alkylene group and dialkyl carbonate having 1 to 4 carbon atoms in the alkyl group, and these carbonates are A mixed solvent occupying 70% by volume or more is preferable because of high electrical conductivity of the electrolytic solution and high cycle characteristics and large current discharge characteristics. Specific examples of the alkylene carbonate having 2 to 4 carbon atoms in the alkylene group include, for example, ethylene carbonate, propylene carbonate, butylene carbonate and the like. Among these, ethylene carbonate and propylene carbonate are preferable.

  Specific examples of the dialkyl carbonate having 1 to 4 carbon atoms in the alkyl group include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl n-propyl carbonate, and ethyl n-propyl carbonate. Etc. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferred.

  As another preferred non-aqueous solvent embodiment, a solvent containing one or two or more solvents having a relative dielectric constant of 25 or more in a proportion of 60% by volume or more, particularly 85% or more has a relatively high boiling point. Even in high temperature use, there are few problems of volatilization and liquid leakage, which is preferable. Examples of the non-aqueous solvent having a relative dielectric constant of 25 or more include ethylene carbonate, propylene carbonate, γ-butyrolactone, and γ-valerolactone, and those containing ethylene carbonate are particularly preferable. In addition, a mixed solvent occupying 55% by volume or more of γ-butyrolactone, or a mixed solvent occupying 30% by volume or more of ethylene carbonate and 30% by volume or more of propylene carbonate generates less gas during high-temperature storage, and cycle characteristics and high current discharge. The balance of characteristics and the like is good and more preferable.

  In the non-aqueous electrolyte solution of the present invention, other useful compounds, for example, conventionally known additives, dehydrating agents, and deoxidizing agents may be mixed and used. For example, conventionally known additives such as fluorinated carbonates such as fluoroethylene carbonate and trifluoropropylene carbonate, 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3 -When nitrogen-containing compounds such as dimethyl-2-imidazolidinone and N-methylsuccinimide are contained in an amount of 0.1 to 5% by weight, capacity retention characteristics and cycle characteristics are improved as compared with the case where they are not contained. Better.

Furthermore, a surfactant may be added in the range of 0.01 to 2% by weight to the non-aqueous electrolyte solution in order to improve the coatability with the separator and the electrode material. A lithium salt is used as the solute of the non-aqueous electrolyte used in the present invention. The lithium salt is not particularly limited as long as it can be used as a solute, and specific examples thereof include an inorganic lithium salt selected from LiClO ₄ , LiPF ₆ , and LiBF ₄ , 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), 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 Examples thereof include fluorine-containing organic lithium salts such as ₂ (CF ₃ SO ₂ ) ₂ and LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ . Among these, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiN (C ₂ F ₅ SO ₂ ) ₂ are preferable in terms of solubility, ion dissociation degree, and electrical conductivity characteristics. LiPF ₆ and LiBF ₄ are more preferable. These solutes may be used in combination of two or more.

Also, two types of inorganic lithium salt selected from LiPF ₆ or LiBF ₄ and fluorine-containing organic lithium salt selected from LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ or LiN (C ₂ F ₅ SO ₂ ) ₂ Use of the above lithium salt in combination tends to suppress deterioration after high-temperature storage, which is preferable. When a nonaqueous solvent containing 60% by weight or more of γ-butyrolactone is selected as the nonaqueous solvent, LiBF ₄ is preferably 50% by weight or more of the entire lithium salt.

  The concentration of the solute lithium salt in the non-aqueous electrolyte is preferably 0.5 to 3 mol / liter. If the concentration is too high or too low, the electric conductivity of the electrolytic solution is low, and the battery performance tends to deteriorate. Materials for the negative electrode constituting the secondary battery of the present invention include carbonaceous materials capable of occluding and releasing lithium, such as organic pyrolysis products, artificial graphite, and natural graphite under various pyrolysis conditions, tin oxide, oxidation A metal oxide material capable of inserting and extracting lithium such as silicon, lithium metal, and various lithium alloys can be used. Two or more kinds of these negative electrode materials may be mixed and used.

  Specific examples of the carbonaceous material capable of occluding and releasing lithium include pyrolysates of organic matter under various pyrolysis conditions, artificial graphite, natural graphite, and the like. Preferably, artificial graphite and purified natural graphite produced by high-temperature heat treatment of graphitizable pitch obtained from various raw materials, or materials obtained by subjecting these graphite to various surface treatments including pitch are mainly used.

  The graphite material 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. Is preferred. The ash content is preferably 1% by weight or less, more preferably 0.5% by weight or less, and particularly preferably 0.1% by weight or less. The crystallite size (Lc) determined by X-ray diffraction by the Gakushin method is preferably 30 nm or more, more preferably 50 nm or more, and particularly preferably 100 nm or more.

Further, the median diameter of the carbonaceous material powder by the laser diffraction / scattering method is preferably 1 to 100 μm, more preferably 3 to 50 μm, still more preferably 5 to 40 μm, and 7 to 30 μm. Is particularly preferred. BET specific surface area is preferably from 0.3~25.0m ² / g, more preferably from 0.5 to 20.0 m ² / g, in 0.7~15.0m ² / g More preferably, it is 0.8-10.0 m < ² > / g. Furthermore, the powder which has been adjusted in the radial case of Raman spectrum analysis using argon ion laser light, the range of the peak P _A (peak intensity I _A) and 1300～1400Cm ^-1 ranging 1570～1620Cm ^-1 the intensity ratio R = I _B / I _a of the peak P _B (peak intensity I _B) is preferably 0.01 to 0.7, the half-value width of the peak in the range of 1570～1620Cm ^-1 is 26cm ^-1 or less, particularly 25cm ^-1 or less is preferable.

  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, etc. to the negative electrode material as necessary to form a slurry, applying the slurry to a substrate of the current collector, and drying. In addition, 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.

  The binder used for manufacturing the electrode is not particularly limited as long as it is a material that is stable with respect to the solvent and the electrolyte used in manufacturing the electrode. Specific examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene / butadiene rubber, isoprene rubber, and butadiene rubber. Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein.

  Examples of the conductive material include metal materials such as copper and nickel, and carbon materials such as graphite and carbon black. The negative electrode current collector is made of a metal such as copper, nickel, and stainless steel. Among these, a copper foil is preferable from the viewpoint of easy processing into a thin film and cost. As a material of the positive electrode constituting the secondary battery of the present invention, a material capable of inserting and extracting lithium such as lithium transition metal composite oxides such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide is used. be able to.

  It does not specifically limit about the manufacturing method of a positive electrode, It can manufacture according to said manufacturing method of a negative electrode. As for the shape, a binder, a conductive material, a solvent and the like are added to the positive electrode material as necessary and mixed, and then applied to the substrate of the current collector to form a sheet electrode, or subjected to press molding to a pellet electrode It can be. As a material of the positive electrode current collector, a metal such as aluminum, titanium, or tantalum or an alloy thereof is used. Of these, aluminum or an alloy thereof is particularly lightweight, which is desirable in terms of energy density.

  The material and shape of the separator used in the secondary battery of the present invention are not particularly limited. However, it is preferable to select from materials that are stable with respect to the electrolytic solution and have excellent liquid retention properties, and it is preferable to use a porous sheet or a nonwoven fabric made of a polyolefin such as polyethylene or polypropylene. The method for producing the secondary battery of the present invention having at least a negative electrode, a positive electrode, and a non-aqueous electrolyte is not particularly limited, and can be appropriately selected from commonly employed methods.

  In addition, the shape of the battery is not particularly limited, and a cylinder type in which a sheet electrode and a separator are spiraled, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, a coin type in which a pellet electrode and a separator are stacked, and the like are used Is possible.

Next, specific examples of the present invention will be further described with reference to examples and comparative examples, but the present invention is not limited to these examples unless it exceeds the gist.
Example 1
The d value of the lattice plane (002 plane) in X-ray diffraction is 0.336 nm, the crystallite size (Lc) is 100 nm or more (652 nm), the ash content is 0.07 wt%, the median diameter by laser diffraction / scattering method is 12 μm, BET specific surface area of 7.5 m ² / g, a peak in the range of the peak P _a (peak intensity I _a) and 1300～1400Cm ^-1 ranging 1570～1620Cm ^-1 in the Raman spectrum analysis using an argon ion laser beam P _B to 94 parts by weight of natural graphite powder intensity ratio R = I _B / I _a is the half width of the peak in the range of 0.12,1570～1620Cm ^-1 is 19.9Cm ^-1 of (peak intensity I _B) A mixture of 6 parts by weight of polyvinylidene fluoride, dispersed in N-methyl-2-pyrrolidone and made into a slurry is uniformly applied onto a negative electrode current collector 18 μm thick copper foil. And, after drying, the negative electrode layer density is pressed so that the 1.5 g / cm ³ by a press machine, then the negative electrode was punched into a disc having a diameter of 12.5 mm.

As a positive electrode active material, 6 parts by weight of carbon black and 9 parts by weight of polyvinylidene fluoride (made by Kureha Chemical Co., Ltd., trade name KF-1000) are added to 85 parts by weight of LiCoO ₂ and mixed, and dispersed with N-methyl-2-pyrrolidone Then, the slurry was uniformly applied onto a 20 μm-thick aluminum foil as a positive electrode current collector, dried, and then pressed with a pressing machine so that the positive electrode layer density was 3.0 g / cm ³ . Thereafter, it was punched into a disk shape having a diameter of 12.5 mm to obtain a positive electrode.

The electrolyte used was LiPF ₆ that had been sufficiently dried under a dry argon atmosphere as a solute, and 2 wt% biphenyl and 1 wt% vinylene carbonate in a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio). %, 1,3-propane sultone was added at a rate of 0.5% by weight, and LiPF ₆ was further dissolved at a rate of 1 mol / liter.

Using the negative electrode, the positive electrode, and the electrolytic solution, the positive electrode was accommodated in a stainless steel can that also serves as a positive electrode conductor, and the negative electrode was placed thereon via a separator impregnated with the electrolytic solution. The can body and a sealing plate that also serves as the negative electrode conductor were caulked and sealed via an insulating gasket to produce a coin-type battery.
Comparative Example 1
Using an electrolytic solution prepared by adding biphenyl to a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio) at a rate of 2% by weight and further dissolving LiPF ₆ at a rate of 1 mol / liter. A coin-type battery was produced in the same manner as in Example 1 except for the above.

Comparative Example 2
2% by weight of biphenyl and 0.5% by weight of 1,3-propane sultone were added to a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio), and LiPF ₆ was further added at 1 mol / liter. A coin-type battery was produced in the same manner as in Example 1 except that an electrolytic solution prepared by dissolving at a ratio was used.

Example 2
2% by weight of biphenyl, 1% by weight of vinylene carbonate, 0.5% by weight of 1,3-propane sultone and 2% by weight of fluorobenzene in a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio) A coin-type battery was fabricated in the same manner as in Example 1 except that an electrolytic solution prepared by adding LiPF ₆ at a rate of 1 mol / liter was added.

Example 3
2% by weight of biphenyl, 1% by weight of vinylene carbonate, 0.5% by weight of 1,3-propane sultone and 2% by weight of heptane in a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio) A coin-type battery was fabricated in the same manner as in Example 1 except that an electrolytic solution prepared by adding LiPF ₆ at a rate of 1 mol / liter was added.

Example 4
2% by weight of cyclohexylbenzene, 1% by weight of vinylene carbonate and 0.5% by weight of 1,3-propane sultone are added to a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio), A coin-type battery was produced in the same manner as in Example 1 except that an electrolytic solution prepared by dissolving LiPF ₆ at a rate of 1 mol / liter was used.

Comparative Example 3
An electrolytic solution prepared by adding cyclohexylbenzene at a ratio of 2% by weight to a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio) and further dissolving LiPF ₆ at a ratio of 1 mol / liter was used. A coin-type battery was produced in the same manner as in Example 1 except that.

Example 5
2% by weight of cyclohexylbenzene, 1% by weight of vinylene carbonate, 0.5% by weight of 1,3-propane sultone and 2% by weight of fluorobenzene in a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio) A coin-type battery was prepared in the same manner as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ at a rate of 1 mol / liter was used.

Example 6
2% by weight of biphenyl, 1% by weight of vinylene carbonate and 0.5% by weight of dimethyl sulfone are added to a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio), and 1 mol / liter of LiPF ₆ is further added. A coin-type battery was produced in the same manner as in Example 1 except that an electrolyte prepared by dissolving at a liter ratio was used.

Example 7
2 wt% biphenyl, 1 wt% vinylene carbonate and 0.5 wt% methyl methanesulfonate were added to a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio), and LiPF ₆ was further added. A coin-type battery was produced in the same manner as in Example 1 except that an electrolyte prepared by dissolving at a rate of 1 mol / liter was used.

Example 8
2% by weight of biphenyl, 0.2% by weight of succinic anhydride, and 0.5% by weight of 1,3-propane sultone are added to a mixture of ethylene carbonate and ethyl methyl carbonate (3: 7 volume ratio). Further, a coin-type battery was fabricated in the same manner as in Example 1 except that an electrolytic solution prepared by dissolving LiPF ₆ at a rate of 1 mol / liter was used.

[Battery evaluation]
Each battery was stabilized by charging and discharging for 5 cycles at a constant current of 0.5 mA at 25 ° C. with a charge end voltage of 4.2 V and a discharge end voltage of 3 V, and then stored in a charged state at 85 ° C. for 3 days. The stored battery was discharged at 25 ° C. with a constant current of 0.5 mA to a discharge end voltage of 3 V, and the remaining capacity was measured. Next, with a constant current of 0.5 mA, the charge end voltage was 4.2 V and the discharge end voltage was 3 V. The capacity after storage was measured by charging and discharging. Next, after charging under the same conditions, the battery was discharged to 3 V at a current value corresponding to 1.5 C, and the high load discharge characteristics were measured (where 1 C represents a current value that can be fully charged in one hour. 5C represents a current value 1.5 times that).

  Table 1 shows the remaining capacity after storage, the capacity after storage, and the capacity at high load discharge when the discharge capacity before storage is 100.

  As is apparent from Table 1 above, the battery of the present invention has a well-balanced improvement in the remaining capacity after storage with respect to the discharge capacity before storage, the subsequent capacity, and the high-load discharge characteristics. It is effective for improvement.

Claims (6)

A non-aqueous electrolyte solution for a non-aqueous electrolyte secondary battery comprising at least a negative electrode capable of inserting and extracting lithium and a positive electrode, wherein the non-aqueous electrolyte solution comprises at least a non-aqueous solvent and a lithium salt. Configured,
In a non-aqueous solvent, cyclohexylbenzene, at least one compound selected from the group consisting of a cyclic carbonate having an unsaturated bond and an acid anhydride, ethyl methyl carbonate,
Cyclic sulfite which is ethylene sulfite, propylene sulfite, butylene sulfite, vinylene sulfite or tetrahydrofuran sulfite;
Chain sulfite which is dimethyl sulfite, diethyl sulfite, ethyl methyl sulfite, methyl propyl sulfite or ethyl propyl sulfite;
A halide of the cyclic sulfite or chain sulfite;
Cyclic sulfone which is sulfolane, 2-methylsulfolane, 3-methylsulfolane, 2-ethylsulfolane, 3-ethylsulfolane, 2,4-dimethylsulfolane, sulfolene, 2-methylsulfolene or 3-methylsulfolene;
A linear sulfone which is dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methyl propyl sulfone, ethyl propyl sulfone, divinyl sulfone, methyl vinyl sulfone, diphenyl sulfone or dibenzyl sulfone;
A halide of the cyclic sulfone or chain sulfone;
Cyclic sulfonic acid which is 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 1,3-butane sultone, 3-phenyl-1,3-propane sultone or 4-phenyl-1,4-butane sultone ester;
Methyl methanesulfonate, ethyl methanesulfonate, propyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, propyl ethanesulfonate, methyl benzenesulfonate, ethyl benzenesulfonate, propyl benzenesulfonate, phenyl methanesulfonate, A chain sulfonate ester which is phenyl ethanesulfonate, phenyl propanesulfonate, methyl benzylsulfonate, ethyl benzylsulfonate, propyl benzylsulfonate, benzyl methanesulfonate, benzyl ethanesulfonate, benzyl propanesulfonate or busulfan;
A halide of the cyclic sulfonate ester or chain sulfonate ester;
Ethylene glycol sulfate, 1,2-propanediol sulfate, 1,3-propanediol sulfate, 1,2-butanediol sulfate, 1,3-butanediol sulfate, 2,3-butanediol sulfate or A cyclic sulfate which is phenylethylene glycol sulfate;
Dimethyl sulfate, diethyl sulfate, ethyl methyl sulfate, methyl propyl sulfate, ethyl propyl sulfate, methyl phenyl sulfate, ethyl phenyl sulfate, phenyl propyl sulfate, benzyl methyl sulfate or benzyl ethyl sulfate; Containing at least one sulfur-containing organic compound selected from the group consisting of halides of chain sulfates,
The content of at least one compound selected from the group consisting of a cyclic carbonate having an unsaturated bond and an acid anhydride in a non-aqueous solvent is 0.01 to 5% by weight, and the content of a sulfur-containing organic compound is A nonaqueous electrolytic solution for a secondary battery, characterized by being 0.01 to 5% by weight. Sulfur-containing organic compounds
Cyclic sulfonic acid which is 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 1,3-butane sultone, 3-phenyl-1,3-propane sultone or 4-phenyl-1,4-butane sultone ester;
Methyl methanesulfonate, ethyl methanesulfonate, propyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, propyl ethanesulfonate, methyl benzenesulfonate, ethyl benzenesulfonate, propyl benzenesulfonate, phenyl methanesulfonate, A chain sulfonate ester which is phenyl ethanesulfonate, phenyl propanesulfonate, methyl benzylsulfonate, ethyl benzylsulfonate, propyl benzylsulfonate, benzyl methanesulfonate, benzyl ethanesulfonate, benzyl propanesulfonate or busulfan; and 2. The nonaqueous secondary battery according to claim 1, which is at least one compound selected from the group consisting of the cyclic sulfonate ester or the chain sulfonate ester halide. The electrolytic solution. Sulfur-containing organic compounds
Cyclic sulfonic acid which is 1,3-propane sultone, 1,4-butane sultone, 2,4-butane sultone, 1,3-butane sultone, 3-phenyl-1,3-propane sultone or 4-phenyl-1,4-butane sultone The nonaqueous electrolytic solution for a secondary battery according to claim 2, which is at least one compound selected from the group consisting of: an ester; and a halide of the cyclic sulfone ester. Sulfur-containing organic compounds
Cyclic sulfone which is sulfolane, 2-methylsulfolane, 3-methylsulfolane, 2-ethylsulfolane, 3-ethylsulfolane, 2,4-dimethylsulfolane, sulfolene, 2-methylsulfolene or 3-methylsulfolene;
A dimethyl sulfone, a diethyl sulfone, an ethyl methyl sulfone, a methyl propyl sulfone, an ethyl propyl sulfone, a divinyl sulfone, a methyl vinyl sulfone, a diphenyl sulfone, or a chain sulfone that is a dibenzyl sulfone; The non-aqueous electrolyte solution for secondary batteries according to claim 1, which is at least one compound selected from the group.   The nonaqueous electrolytic solution for a secondary battery according to any one of claims 1 to 4, wherein the content of the sulfur-containing organic compound in the nonaqueous solvent is 0.01 to 3% by weight. At least lithium can the absorbing and releasing negative electrode, positive electrode and the nonaqueous electrolyte secondary battery including a nonaqueous electrolytic solution according to any one of claims 1-5.