KR20060116852A - Nonaqueous electrolyte and nonaqueous electrolyte secondary battery - Google Patents

Abstract

Disclosed is a nonaqueous electrolyte secondary battery wherein safety during overcharge is further improved. Specifically disclosed is a nonaqueous electrolyte secondary battery having such a structure that an electrode group (3) including a positive electrode (10), a negative electrode (11) and a separator (12) is arranged within a space hermetically sealed by a container body (2) and a covering plate (4), and a nonaqueous electrolyte is injected into the electrode group(3). In this secondary battery, it is used a nonaqueous electrolyte obtained by dissolving an electrolyte in a nonaqueous solvent which contains halogenated benzenes while having the aminated benzene content, as impurities, of less than 100 ppm.

Description

Non-aqueous electrolyte and non-aqueous electrolyte secondary battery {NONAQUEOUS ELECTROLYTE AND NONAQUEOUS ELECTROLYTE SECONDARY BATTERY}

The present invention relates to a nonaqueous electrolyte and a nonaqueous electrolyte secondary battery.

Recently, as electronic devices such as mobile communication devices, notebook PCs, palmtop PCs, integrated video cameras, portable CD (MD) players, cordless telephones, etc. have been miniaturized and reduced in weight, power supply of these electronic devices is particularly small and large. Phosphorus battery is required.

Examples of batteries that are popularized as power sources for these electronic devices include secondary batteries such as alkaline manganese batteries, nickel cadmium batteries, and lead-acid batteries. Among them, a nonaqueous electrolyte secondary battery using a lithium composite oxide as a positive electrode and a carbonaceous material capable of occluding and releasing lithium ions at a negative electrode has a small size, light weight, high unit cell voltage, and high energy density. It is attracting attention from the thing.

By the way, in recent batteries, it is becoming more difficult to maintain safety at the time of overcharging, to increase the battery temperature, and to prevent the thermal runaway of the battery, accompanied by high energy density. Prior literatures and patent documents related to safety at the time of overcharging have been known so far, and the centers are improving the structure of the battery and making it safer, and improving the safety by adding an overcharge additive to the nonaqueous electrolyte. Especially, when adding an overcharge additive to a nonaqueous electrolyte, since the structural constraint is few, the various is proposed.

As an overcharge additive, benzene which has a methyl group and a methoxy group, such as 4-methoxytoluene, 2,6-methoxytoluene, 3,4,5-trimethoxytoluene, has a redox potential of about 4.8-4.9V. In redox shuttles are known (see, for example, Japanese Patent Laid-Open No. 7-302614).

Furthermore, benzenes having an alkyl group and a halogen atom, such as 2-chloro-p-xylene and 4-bromo-m-xylene, are known (see, for example, Japanese Patent Application Laid-Open No. 9-50822). In Examples of Japanese Patent Laid-Open No. 9-50822, it is described that the exothermic starting voltage of a battery in which such benzenes are added to the nonaqueous electrolyte is in the range of 4.45 to 4.75V.

Furthermore, benzenes in which a halogen atom and an alkoxy group are substituted, such as 1,2-dimethoxybenzene and 1,2-dimethoxy-4-fluorobenzene, are known (see, for example, Japanese Patent Application Laid-Open No. 2000-156243). ).

Benzene described in Japanese Patent Application Laid-Open No. 7-302614, Japanese Patent Application Laid-Open No. 9-50822, and Japanese Patent Application Laid-Open No. 2000-156243 is a positive electrode at the time of full charge of a nonaqueous electrolyte battery. It has a reversible redox potential at a cell potential that is more precious than the potential, and by adding these to the nonaqueous electrolyte, the oxidative decomposition reaction of the nonaqueous solvent generated in an overcharged state is promoted, and the heat generated by the oxidative decomposition reaction is utilized. Overcharge current is cut off.

Moreover, it is proposed to contain benzene which has a fluorine atom and a C1-C10 hydrocarbon group in a nonaqueous electrolyte (for example, refer Unexamined-Japanese-Patent No. 11-329496). Japanese Patent Laid-Open No. 11-329496 discloses that the benzenes suppress the exothermic reaction by suppressing the reaction rate between the positive electrode and the nonaqueous electrolyte.

Furthermore, lithium salt as an electrolyte, 20 to 60% by volume of ethylene carbonate, 20 to 70% by volume of dialkyl carbonate, and 5 to 5 fluorinated toluene (2-fluorotoluene, 3-fluorotoluene, 4-fluorotoluene, etc.) An organic electrolyte solution containing an organic solvent containing 30% by volume is proposed (see, for example, Japanese Patent Application Laid-Open No. 2001-256996). According to Japanese Unexamined Patent Application Publication No. 2001-256996, by using the organic electrolyte solution, the increase in the internal pressure of the battery when left at high temperature for a long time is suppressed, and the breakage of the battery, particularly the vent part, is prevented and the stability of the battery is improved. do.

Thus, Japanese Patent Laid-Open No. 7-302614, Japanese Patent Laid-Open No. 9-50822, Japanese Patent Laid-Open No. 2000-156243, Japanese Patent Laid-Open No. 11-329496 and Japanese Patent Laid-Open No. 2001-256996. For example, it is described that the safety, stability, and the like of a battery are improved by adding benzenes having a methyl group, a methoxy group, a halogen atom or the like to a nonaqueous electrolyte (or a nonaqueous electrolyte) on a benzene ring. However, there is an urgent need for a battery in which safety at the time of overcharging is further improved.

In addition, Japanese Patent Laid-Open No. 7-302614, Japanese Patent Laid-Open No. 9-50822, Japanese Patent Laid-Open No. 2000-156243, Japanese Patent Laid-Open No. 11-329496, Japanese Patent Laid-Open No. 2001-256996 In neither case, there is no description regarding impurity components contained in the nonaqueous electrolyte.

An object of the present invention is to provide a nonaqueous electrolyte and a nonaqueous electrolyte secondary battery having a significantly high safety upon overcharging.

The inventors of the present invention, in the non-aqueous electrolyte containing a benzene having a methyl group and a halogen atom as an overcharge additive which has an action of preventing the charging of the battery further progress in the course of research to solve the above problems, the benzene It has been found that aminated benzenes, which are raw materials for the production of ethylene, exist as impurities and adversely affect the safety during overcharging of batteries.

As a result of further studies based on these findings, the inventors have found that the content of the amino benzenes in the nonaqueous electrolyte has a particularly significant effect on the safety during overcharging of the nonaqueous electrolyte secondary battery, and the present invention has been completed.

In the nonaqueous electrolyte containing the nonaqueous solvent and the electrolyte, the present invention is a nonaqueous electrolyte, wherein the nonaqueous solvent contains halogenated benzenes, and the content of aminated benzenes contained as impurities in the nonaqueous solvent is less than 100 ppm. .

The nonaqueous electrolyte of the present invention is also characterized in that the nonaqueous solvent described above contains carbonates and / or γ-butyrolactone together with halogenated benzenes.

Furthermore, the nonaqueous electrolyte of the present invention is characterized in that the halogenated benzenes described above are at least one selected from halogenated toluene and halogenated xylene having one or two or more chlorine atoms and / or fluorine atoms.

Furthermore, the nonaqueous electrolyte of the present invention is characterized in that the halogenated benzenes described above are at least one selected from o-chlorotoluene, p-chlorotoluene and o-fluorotoluene.

Furthermore, the non-aqueous electrolyte of this invention is characterized in that the above-mentioned amino benzene is at least 1 sort (s) chosen from aminated toluene and an amino xylene.

Furthermore, the non-aqueous electrolyte of this invention is characterized in that the above-mentioned amino benzene is at least 1 sort (s) chosen from 2-aminotoluene, 4-aminotoluene, and amino xylene.

The present invention also provides a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and any of the nonaqueous electrolytes described above.

The objects, features, and advantages of the present invention will become more apparent from the following detailed description and drawings.

To practice the invention  Best form for

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[Non-aqueous electrolyte]

The nonaqueous electrolyte of the present invention comprises a nonaqueous solvent and an electrolyte, wherein the nonaqueous solvent contains halogenated benzenes and aminated benzenes as impurities, and the content of aminated benzenes in the nonaqueous solvent is less than 100 ppm. .

In the nonaqueous electrolyte of the present invention, preferably, the nonaqueous solvent contains carbonates and / or γ-butyrolactone together with halogenated benzenes. Carbonates and (gamma) -butyrolactone can improve the ion conductivity, redox stability, etc. of a nonaqueous electrolyte.

Since the nonaqueous electrolyte of the present invention has a relatively low reactivity with the positive electrode during overcharging, the reaction between the positive electrode and the nonaqueous electrolyte terminates quickly after the current is blocked. Therefore, the nonaqueous electrolyte secondary battery can be avoided from reaching thermal runaway.

In the nonaqueous electrolyte of the present invention, known halogenated benzenes in the nonaqueous solvent can be used. Among them, halogenated benzenes each having one or two or more halogen atoms and methyl groups as substituents on the benzene ring are preferable. . Among such halogenated benzenes, halogenated toluene, halogenated xylene, and the like are preferable. Moreover, as a halogen atom, chlorine and fluorine are preferable. Iodine and bromine are undesirable because they are easy to decompose in the battery.

Specific examples of the halogenated toluene include o-chlorotoluene, m-chlorotoluene, p-chlorotoluene, o-fluorotoluene, m-fluorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5 -Dichlorotoluene, 2,6-dichlorotoluene, 3,4-dichlorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,6-di And halogenated toluene in which one or two halogen atoms are substituted by one or two halogen atoms on a benzene ring such as fluorotoluene, 2-chloro-4-fluorotoluene, and 2-chloro-6-fluorotoluene. .

Specific examples of the halogenated xylene include 2-chloro-p-xylene, 2-chloro-m-xylene, 3-chloro-o-xylene, 4-chloro-o-xylene, 2,5-dichloro-p-xylene, 2- Benzene rings, such as fluoro-p-xylene, 2-fluoro-m-xylene, 3-fluoro-o-xylene, 4-fluoro-o-xylene, 2,5-difluoro-p-xylene And halogenated xylenes in which one, two or more halogen atoms have been substituted on the phase.

Halogenated benzenes can be used individually by 1 type, and can also use 2 or more types together.

The content in the non-aqueous solvent of the halogenated benzenes is not particularly limited, but is preferably 0.1 to 15% by weight, more preferably 0.5 to 10% by weight, particularly preferably 1 to 8% by weight of the total amount of the nonaqueous solvent.

Known carbonates may be used as the carbonates used together with the halogenated benzenes, and examples thereof include cyclic carbonates and chain carbonates.

As cyclic carbonate, ethylene carbonate, propylene carbonate, etc. are used preferably. As the chain carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and the like are preferably used.

Carbonates can be used individually by 1 type, or can use 2 or more types together.

The content of the carbonates in the nonaqueous solvent is not particularly limited, but the content of ethylene carbonate is preferably 19.9 to 59.9% by weight of the total amount of the nonaqueous solvent, more preferably 25 to 50% by weight, particularly preferably 25 to 45 Weight percent. If it is less than 19.9 weight% largely, in the secondary battery containing the nonaqueous electrolyte of this invention, there exists a possibility that it may become impossible to suppress reaction of the negative electrode and nonaqueous electrolyte especially in high temperature environment. Moreover, when it exceeds 59.9 weight% significantly, there exists a possibility that the problem, such as being easy to solidify at low temperature, may arise.

The content in the non-aqueous solvent of γ-butyrolactone used with halogenated benzenes is not particularly limited, but is preferably 40 to 80% by weight of the total amount of the nonaqueous solvent, more preferably 50 to 80% by weight, Especially preferably, it is 55 to 75 weight%.

In the present invention, one kind of carbonates or? -Butyrolactone can be used alone, but a combination of two or more kinds of carbonates or a combination of carbonates and? -Butyrolactone is preferable.

In particular, in the secondary battery containing the nonaqueous electrolyte of the present invention, a combination of a cyclic carbonate and a linear carbonate, a combination of two or more cyclic carbonates, and the like are preferable from the viewpoint of improving the capacity retention rate at high temperature storage. From the viewpoint of suppressing the gas generation at the time of high temperature storage, the combination of cyclic carbonate and (gamma) -butyrolactone, the combination of 2 or more types of cyclic carbonate, etc. are preferable. From the viewpoint of safety improvement, a combination of cyclic carbonate and γ-butyrolactone is preferable. Moreover, from the viewpoint of both high temperature storage characteristics and safety, a combination of ethylene carbonate and γ-butyrolactone, a combination of ethylene carbonate and propylene carbonate, a combination of ethylene carbonate and ethyl methyl carbonate, ethylene carbonate and ethyl methyl carbonate and di Combinations with ethyl carbonate and the like are preferred.

In the nonaqueous electrolyte of the present invention, aminated benzenes contained in the nonaqueous solvent as impurities are benzenes having an amino group as a substituent on the benzene ring. Although many of such benzenes are known, among these, benzenes having an amino group and one or two or more methyl groups as substituents on the benzene ring, such as aminated toluene and aminated xylene, contain the nonaqueous electrolyte of the present invention. It has been found by the inventor's research that the secondary battery has a particularly bad influence on the safety during overcharging.

Any of the aminated toluene and the xylated axylene is used as a raw material of halogenated benzenes, and is likely to remain unreacted in the halogenated toluene and the xylene halide depending on the reaction conditions and the degree of purification. Commercially available halogenated benzenes generally include aminated toluene and / or aminated xylene. For example, in the o-fluorotoluene manufactured by Wako Pure Chemical Industries, Ltd., 2-aminotoluene (o-toluidine) remained at 1000 ppm.

As a specific example of aminated toluene, 2-aminotoluene, 3-aminotoluene, 4-aminotoluene, 2,3-diaminotoluene, 2,4-diaminotoluene, 2,5-diaminotoluene, 2,6- Diaminotoluene, 3,4-diaminotoluene, and the like.

Moreover, as a specific example of amination xylene, 2-amino-p-xylene, 2-amino-m-xylene, 3-amino-o-xylene, 4-amino-o-xylene, 2,5-diamino-p- Xylene etc. are mentioned.

Amino acid toluene and an amino acid xylene may be contained in 1 type (s) or 2 or more types, respectively, in a nonaqueous solvent. Moreover, 1 type, or 2 or more types of amino-ized toluene and 1 type, or 2 or more types of amino xylene may be simultaneously contained in a nonaqueous solvent.

It is essential that content in the non-aqueous solvent of aminated benzenes is less than 100 ppm as the total amount, More preferably, it is 50 ppm or less. When 100 ppm or more is contained in a nonaqueous solvent, the secondary battery containing the nonaqueous electrolyte of this invention WHEREIN: The frequency of abnormal heat generation at the time of overcharge becomes high, and there exists a possibility that safety may fall.

In order to make content in the non-aqueous solvent of aminated benzenes less than 100 ppm, what is necessary is just to highly refine | purify halogenated benzenes, for example. As a method of highly purified, distillation purification can be applied with respect to halogenated benzenes whose melting point is less than 50 degreeC. In that case, it is preferable to use the installation which has the distillation capacity of 5 or more distillation stages. Regarding halogenated benzenes having a melting point of 50 ° C. or higher, purification by crystallization can be applied.

The nonaqueous solvent in the nonaqueous electrolyte of the present invention contains halogenated benzenes as essential components, and preferably contains carbonates and / or γ-butyrolactone together with halogenated benzenes.

In the nonaqueous electrolyte of the present invention, solvents other than the nonaqueous solvent can be used as the subcomponent as well as the nonaqueous solvent. As the subcomponent, any of those used in the nonaqueous electrolyte for secondary batteries can be used. For example, vinylene carbonate, vinyl ethylene carbonate, phenyl ethylene carbonate, γ-valerolactone, methyl propionate, ethyl propionate, ethyl acetate, aceto Nitoryl, 2-methylfuran, furan, thiophene, catecholcarbonate, ethylene sulfite, 12-crown-4, tetraethylene glycol dimethyl ether, 1,3-propanesultone, anhydrous sulfobenzoic acid, divinyl sulfone, 3- Hydroxy-1-propenesulfonic acid-γ-sultone, tris (trioctyl) phosphate, and the like.

Among these subcomponents, vinylene carbonate, 1,3-propanesultone, sulfobenzoic anhydride, divinyl sulfone, 3-hydroxy-1-propenesulfonic acid-γ-sultone and the like are secondary containing the nonaqueous electrolyte of the present invention. In the battery, since a dense protective film is formed on the surface of the negative electrode, it is possible to further lower the reactivity between the negative electrode and the non-aqueous electrolyte and to improve the discharge discharge characteristics and stability at high temperature storage. A subcomponent can be used individually by 1 type, and can use 2 or more types together.

Although the usage-amount of a subcomponent is not restrict | limited, Preferably it is selected from the range of 10 weight% or less with respect to the total weight of a non-aqueous solvent, More preferably, it is 0.01-5 weight%, Especially preferably, it is 0.1-3 weight% Do. If more than 10 wt% of the subcomponent is used, the ion permeability of the protective film on the negative electrode surface is lowered, and there is a possibility that the low-temperature discharge characteristics are greatly impaired.

As the electrolyte dissolved in the non-aqueous solvent, those commonly used in this field can be used. For example, lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), or hexafluorofluoride. Lithium bisoridium (LiAsF ₆ ), lithium trifluoromethsulfonate (LiCF ₃ SO ₃ ), bistrifluoromethylsulfonylimide lithium (LiN (CF ₃ SO ₂ ) ₂ ), bispentafluoroethylsulfonyl imide lithium _{(LiN (C 2 F 5 SO} 2) 2) it includes lithium salts and the like. An electrolyte can be used individually by 1 type and can also use 2 or more types together. In particular, when a mixed salt containing LiBF ₄ and LiPF ₆ is used, the secondary battery containing the nonaqueous electrolyte of the present invention can further improve the cycle life at a high temperature.

The amount of the electrolyte dissolved in the nonaqueous solvent can be appropriately selected from a wide range which is not particularly limited, but is preferably in the range of 0.5 to 2.5 mol / L, more preferably 1 to 2.5 mol / L.

The nonaqueous electrolyte of the present invention can be produced, for example, by adding carbonates and / or γ-butyrolactone to halogenated benzenes to prepare a nonaqueous solvent, and dissolving the electrolyte therein. A nonaqueous electrolyte can be made into a desired form, such as a liquid phase (nonaqueous electrolyte) and a gel form, for example.

The amount of the non-aqueous electrolyte is not particularly limited, but is preferably 0.2 to 0.6 g, more preferably 0.25 to 0.55 g, per 100 mAh battery unit capacity.

[Non-aqueous electrolyte secondary battery]

The nonaqueous electrolyte secondary battery of the present invention is characterized by comprising a positive electrode, a negative electrode, and the nonaqueous electrolyte of the present invention.

That is, the nonaqueous electrolyte secondary battery of this invention can employ | adopt the structure similar to the conventionally well-known nonaqueous electrolyte battery except using the nonaqueous electrolyte of this invention as a nonaqueous electrolyte.

According to the nonaqueous electrolyte secondary battery of the present invention, when the potential of the positive electrode rises due to a failure of the charger of a portable device incorporating the battery and the potential of the positive electrode rises, the separator can be reliably shut down. You can safely shut it down. That is, in the overcharged state, by generating an exothermic reaction by oxidation reaction of halogenated benzenes, the battery temperature can be quickly increased to the shutdown temperature of the separator, so that the overcharge current can be blocked early. Therefore, a smooth oxidation reaction can be performed by making content of amination benzenes less than 100 ppm, and thermal runaway can be avoided by this.

When 100 ppm or more of amino-ized benzene is contained in a nonaqueous solvent, oxidation reaction will begin faster than halogenated benzene, and the exothermic reaction of the whole will be slower than the halogenated benzene compound alone. In such a situation, if the battery temperature does not rise rapidly to the shutdown temperature of the separator, the separator shutdown becomes incomplete, the overcharge current cannot be cut off completely, and if the overcharge current continues to flow, there is a risk of thermal runaway. have.

EMBODIMENT OF THE INVENTION Hereinafter, the nonaqueous electrolyte secondary battery of this invention is demonstrated, referring drawings. 1 is a perspective view schematically showing the configuration of a nonaqueous electrolyte secondary battery 1 which is a first embodiment of the present invention. FIG. 2 is a partial cross-sectional view seen from cut line II-II shown in FIG. 1. FIG.

The nonaqueous electrolyte secondary battery 1 includes a container body 2 formed in a rectangular cup shape, an electrode group 3 housed in the container body 2, and a cover plate 4 sealing the container body 2. ), The positive electrode tab 5 inserted between the container body 2 and the cover plate 4 and connected to the positive electrode 10 in the electrode group 3, the container body 2 and the cover plate ( It is comprised including the negative electrode tab 6 inserted between 4 and connected to the negative electrode 11 in the electrode group 3.

The container body 2 is a laminate comprising an outer protective layer 7, an inner protective layer 8, and a metal layer 9 disposed between the outer protective layer 7 and the inner protective layer 8. It is formed by a film. The outer protective layer 7 and the inner protective layer 8 are resin films containing a thermoplastic resin, preferably a heat resistant thermoplastic resin as a main component. As a specific example of a thermoplastic resin, For example, polyolefin, such as polyethylene, a polypropylene, cyclic polyolefin, a polyamide, polyester, crystalline polyester, a high density polyethylene, a low density polyethylene, a linear low density polyethylene, an ethylene-vinyl acetate copolymer, a poly Acrylonitrile, polyvinylidene chloride, etc. are mentioned. The resin film may be a laminate of resin films containing two or more different thermoplastic resins. As a metal which comprises the metal layer 9, metals, such as aluminum, stainless steel, iron, copper, nickel, titanium, molybdenum, gold, metal oxides, such as a silicon oxide and aluminum oxide, are mentioned, for example. Moreover, although the thickness of a laminated film can be selected suitably from a wide range, Preferably it is 50-300 micrometers. Moreover, the width | variety of the edge part 2a of the container main body 2 becomes wide, and the container main body 2 and the cover plate 4 are adhere | attached by this edge part 2a.

The electrode group 3 is formed by combining the positive electrode 10, the negative electrode 11, and the separator 12. Specifically, in the electrode group 3, a laminate including an anode 10, a cathode 11, and a separator 12 disposed between the anode 10 and the cathode 11 is flat. It is formed into a wound structure.

The positive electrode 10 includes a current collector and a positive electrode layer supported on one or both surfaces of the current collector and containing an active material.

As an electrical power collector, what is normally used in this field can be used, For example, an electroconductive board etc. are mentioned. As a metal which comprises a conductive substrate, aluminum, stainless steel, nickel etc. are mentioned, for example. The conductive substrate may be a porous structure or may be free of holes.

The positive electrode layer contains a positive electrode active material, a conductive agent and a binder.

As the positive electrode active material, those commonly used in this field can be used, and examples thereof include manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel cobalt oxide, lithium-containing iron oxide, and lithium. And metal oxides such as vanadium oxide, chalcogen compounds such as titanium disulfide, and molybdenum disulfide. Among them, lithium-containing cobalt oxide (e.g. LiC00 _2), lithium-containing nickel cobalt oxide (e.g., _{LiNi 0 .8 Co 0 .2 O 2} ), lithium manganese composite oxides (e.g. LiMn ₂ 0 _4, LiMnO ₂ ) is preferable since a high voltage is obtained. A positive electrode active material can be used individually by 1 type, and can also use 2 or more types together.

As the conductive agent, those commonly used in this field can be used, and examples thereof include acetylene black, carbon black, graphite and the like. A conductive agent can be used individually by 1 type, and can use 2 or more types together as needed.

As a binder, what is normally used in this field can be used, For example, polytetrafluoroethylene, polyvinylidene fluoride, polyethersulfone, ethylene-propylene-diene copolymer, styrene-butadiene rubber, etc. are mentioned. . A binder can be used individually by 1 type, or can use 2 or more types together as needed.

It is preferable to make the compounding ratio of a positive electrode active material, a electrically conductive agent, and a binder into the range of 80-95 weight% of positive electrode active materials, 3-20 weight% of conductive agents, and 2-7 weight% of binders.

The positive electrode 10 is produced by, for example, suspending a positive electrode active material, a conductive agent, and a binder in a suitable solvent, applying the suspension to a current collector, drying, and forming a thin plate.

The negative electrode 11 includes a current collector and a negative electrode layer supported on one side or both sides of the current collector.

As an electrical power collector, what is normally used in this field can be used, For example, an electroconductive board etc. are mentioned. As a metal which comprises a conductive substrate, copper, stainless copper, nickel etc. are mentioned, for example. The conductive substrate may be a porous structure or may be free of holes.

The negative electrode layer contains a negative electrode active material and a binder.

As the negative electrode active material, a material that occludes and releases lithium ions can be used. For example, graphite materials such as graphite, coke, carbon fiber, spherical carbon, pyrolytic gaseous carbonaceous material, resinous material, or carbonaceous material, 500-3000 ° C for thermosetting resins, isotropic pitch, mesophase pitch carbon, mesophase pitch carbon fiber, mesophase globules, and the like (particularly, mesophase pitch carbon fiber is preferred due to high capacity and charge / discharge cycle characteristics) Graphite materials or carbonaceous materials obtained by heat treatment at, chalcogenide compounds such as titanium disulfide, molybdenum disulfide, niobium selenide, light metals such as aluminum, aluminum alloys, magnesium alloys, lithium and lithium alloys, or alloys thereof. Can be. Especially, the graphite material containing the graphite crystal whose surface spacing d002 of (002) plane becomes like this. Preferably it is 0.34 nm or less, More preferably, it is 0.337 nm or less. A nonaqueous electrolyte secondary battery having a negative electrode containing such a graphite material as a negative electrode active material significantly improves battery capacity and large current discharge characteristics. A negative electrode active material can be used individually by 1 type, and can use 2 or more types together.

As the binder, those commonly used in this field can be used, and examples thereof include polydetrafluoroethylene, polyvinylidene fluoride, ethylene-propylene-diene copolymer, styrene-butadiene rubber, carboxymethylcellulose, and the like. have. A binder can be used individually by 1 type and can also use 2 or more types together.

It is preferable that the compounding ratio of a negative electrode active material and a binder is the range of 80-98 weight% of carbonaceous substances and 2-20 weight% of binders.

The negative electrode 11 is, for example, mixed with a negative electrode active material and a binder in the presence of a suitable solvent, the resulting suspension is applied to the current collector, dried, and then press once or multistage five to five times at a desired pressure. It is produced by doing.

As the separator 12, those commonly used in this field can be used, and examples thereof include a microporous membrane, a woven fabric, a nonwoven fabric, and a laminate of the same or different materials. In particular, when the temperature of the electrode group 3 rises abnormally due to heat generation due to overcharging or the like, the microporous membrane causes a so-called shutdown phenomenon in which the constituent resin plastically deforms and blocks fine pores, thereby blocking the flow of lithium ions, It is preferable to prevent further heat generation and to terminate the overcharge state safely. Examples of the material for forming the separator 12 include polyethylene, polypropylene, ethylene-propylene copolymers, ethylene-butene copolymers, and the like. These materials can be used individually by 1 type, or can use 2 or more types together.

The electrode group 3 is wound, for example, in (1) the positive electrode 10 and the negative electrode 11 in a flat or vortex shape with a separator 12 therebetween, or (2) the positive electrode 10 And winding the cathode 11 in a vortex with a separator 12 therebetween, compressing it in a radial direction, or (3) separating the separator 12 between the anode 10 and the cathode 11. It is produced by the method which bends one or more times through the interposition, or (4) laminates the positive electrode 10 and the negative electrode 11 with the separator 12 interposed therebetween.

Although it is not necessary to press the electrode group 3, you may press in order to raise the integration strength of the positive electrode 10, the negative electrode 11, and the separator 12. It is also possible to perform heating at the time of pressing.

The electrode group 3 may contain an adhesive polymer compound in order to increase the integration strength of the positive electrode 10, the negative electrode 11, and the separator 12. It is preferable that an adhesive high molecular compound can maintain high adhesiveness in the state holding a nonaqueous electrolyte, and it is more preferable that a lithium ion conductivity is high. Specifically, polyacrylonitrile, polyacrylate, polyvinylidene fluoride, polyvinyl chloride, polyethylene oxide, etc. are mentioned.

The electrode group 3 is impregnated with and retained the nonaqueous electrolyte of the present invention.

The cover plate 4 is attached to a laminate film including an outer protective layer 7, an inner protective layer 8, and a metal layer 9 disposed between the outer protective layer 7 and the inner protective layer 8. Is formed by. As a laminated film, the thing similar to the laminated film of the container main body 2 can be used.

One end of the positive electrode tab 5 is connected to the positive electrode 10, and passes between the container body 2 and the cover plate 4, and the other end 5a is attracted to the outside of the container body 2. It functions as an anode terminal. As a material which comprises the positive electrode tab 5, what is normally used in this field can be used, For example, aluminum, nickel, titanium, etc. are mentioned.

One end of the negative electrode tab 6 is connected to the negative electrode 11, and passes between the container body 2 and the cover plate 4, and the other end 6a is attracted to the outside of the container body 2. It functions as a negative electrode terminal. As a material which comprises the negative electrode tab 6, what is normally used in this field can be used, For example, the laminated body which formed the nickel layer by plating etc. on copper, nickel, copper foil, etc. are mentioned.

The nonaqueous electrolyte secondary battery 1 can be manufactured in the same manner as a conventional battery manufacturing method. For example, the positive electrode tab 5 and the negative electrode tab 6 are connected to the electrode group 3 so that a part of each of the positive electrode tab 5 and the negative electrode tab 6 extends out of the container body 2. The electrode group 3 is placed in the container body 2. Furthermore, the cover plate 4 and the container body 2 are overlapped with each other so that the inner protective layer 8 of the cover plate 4 and the inner protective layer 8 of the edge portion 2a of the container body 2 contact each other. By adhering and fixing the portion by heat sealing or the like, the electrode group 3 is sealed in the container body 2, whereby the nonaqueous electrolyte battery 1 is obtained.

The non-electrolyte secondary battery of the present invention is not limited to the same form as that of the nonaqueous electrolyte battery 1, and can be, for example, a battery having various forms such as a cylindrical shape, a square shape, and a coin type.

The nonaqueous electrolyte secondary battery of the present invention can be used for the same use as that to which a nonaqueous electrolyte secondary battery is conventionally applied. Examples thereof include, for example, various electronic devices, especially portable electronic devices such as mobile communication devices such as mobile phones and mobile phones, portable PCs such as notebook PCs and palmtop PCs, cameras, digital cameras, It can be used suitably as a power supply for an integrated video camera, a portable CD (MD) player, or the like.

1 is a perspective view schematically showing the configuration of a nonaqueous electrolyte secondary battery that is a first embodiment of the present invention.

FIG. 2 is a partial cross-sectional view seen from cut line II-II shown in FIG. 1. FIG.

An Example and a comparative example are given to the following, and this invention is demonstrated to it further more concretely.

(Example 1)

<Production of Anode>

To 90 parts by weight of a lithium cobalt oxide (Li _x C00 ₂ ; where X is 0 <x≤1), 5 parts by weight of acetylene black and 5 parts by weight of a dimethylformamide solution of polyvinylidene fluoride were added and mixed to form a slurry. Prepared. The slurry was applied to both sides of an aluminum foil (anode current collector) having a thickness of 15 μm, dried, and pressed to prepare a positive electrode having a structure in which a positive electrode layer having a thickness of 60 μm was supported on both sides of the current collector.

<Production of Cathode>

95 parts by weight of a powder of mesophase pitch-based carbon fiber (0.300 nm plane spacing d002 of (002) plane required by powder X-ray diffraction) as a carbonaceous material and 5 weights of polyvinylidene fluoride Negative dimethylformamide solution was mixed to prepare a slurry. The slurry was applied to both surfaces of a copper foil (negative current collector) having a thickness of 12 µm, dried, and pressed to prepare a negative electrode having a structure in which a negative electrode layer having a thickness of 55 µm was supported on both surfaces of the current collector.

In addition, the surface spacing d002 of the (002) plane of the carbonaceous substance was determined by the half-value width midpoint method from the powder X-ray diffraction spectrum. At this time, scattering correction such as Lorentz scattering was not performed.

<Separator>

A microporous polyethylene membrane having a thickness of 25 μm and a porosity of 45% was used.

<Production of electrode group>

Ultrasonic welding of the positive electrode lead which consists of strip | belt-shaped aluminum foil (100 micrometers in thickness) to the positive electrode collector, and ultrasonically welding the negative electrode lead which consists of strip | belt-shaped nickel foil (thickness 100 micrometers) to the negative electrode collector, It wound in the vortex shape through the separator in between, and produced the electrode group. The electrode group was molded into a flat shape by pressurizing with a press under heating.

<Preparation of nonaqueous electrolyte amount>

Ethylene carbonate (EC), γ-butyrolactone (GBL), o-chlorotoluene (o-CT; 4.8 V oxidation potential on lithium metal) and tris (trioctyl) phosphate were weight ratios (EC: GBL: o -CT: TOP) was mixed so as to be 35: 59.5: 5: 0.5 to prepare a nonaqueous solvent. Lithium tetrafluoroborate (LiBF ₄ ) was dissolved in the obtained nonaqueous solvent so as to have a concentration of 1.5 mol / L to prepare a nonaqueous electrolyte solution of the present invention. Moreover, the nonaqueous solvent contained 2-aminotoluene as amination benzene from the result of the gas chromatograph analysis, and the content was 30 ppm or less.

<Production of Non-Aqueous Electrolyte Secondary Battery>

The laminated film of thickness 100micrometer which covered both surfaces of aluminum foil with polyethylene was shape | molded in rectangular cup shape with the press, and the electrode group was accommodated in the obtained container.

Subsequently, the electrode group in a container was vacuum-dried at 80 degreeC for 12 hours, and the moisture contained in an electrode group and a laminated film was removed.

After injecting the non-aqueous electrolyte solution into the electrode group in the container so that the amount per 1Ah of the battery capacity is 4.8 g, the same laminated film is placed on the upper surface of the container, and sealed by heat seal. A nonaqueous electrolyte secondary battery of 3.6 mm in thickness, 35 mm in width, 62 mm in height, and nominal capacity of 0.65 Ah was assembled.

The first non-aqueous electrolyte secondary battery was subjected to constant current and constant voltage charging for 15 hours from 0.2C to 4.2V at room temperature as a first charge-discharge step, thereafter discharged from 0.2C to 3.0V at room temperature, and the nonaqueous electrolyte secondary battery was discharged. Manufactured.

Here, 1C is a current value required for discharging the nominal capacity Ah in one hour. Therefore, 0.2C is a current value required for discharging the nominal capacity Ah in 5 hours.

(Examples 2 to 22)

A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the composition of the nonaqueous solvent and the content of the aminated benzenes were changed as shown in Table 1.

In Table 1, o-FT is o-fluorotoluene (4.9V oxidation potential in lithium metal), p-CT is p-chlorotoluene (4.8V oxidation potential in lithium metal), and 2FPX is 2 -Fluoro-p-xylene (4.7 V oxidation potential on large metal lithium).

In Table 1, the TOP of the subcomponent is tris (trioctyl) phosphate, VC is vinylene carbonate, PS is 1,3-propanesultone, SBAH is sulfobenzoic anhydride, DVSU is divinyl sulfone, and PRS is 3-hydroxy. -1-propenesulfonic acid-γ-sultone is shown.

In Table 1, 2-AT of aminated benzene represents 2-aminotoluene, and 2-APX represents 2-amino-p-xylene.

(Comparative Examples 1 to 11)

A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the composition of the nonaqueous solvent and the content of the aminated benzenes were changed as shown in Table 1.

(Test Example 1)

The overcharge test was performed about each of 10 nonaqueous electrolyte secondary batteries obtained in Examples 1-22 and Comparative Examples 1-11. In the overcharge test, charging is continued at a current value of 2C, and the number of nonaqueous electrolyte secondary batteries in which abnormal heat generation or ignition occurs is recorded. Table 1 shows the ratio (abnormal heat generation rate,%) of the total number of batteries in which abnormal heat generation or ignition occurred.

Note: Example 8 used LiBF ₄ and LiPF ₅ in a ratio of 1: 1 (weight ratio) as the electrolyte.

As is apparent from Table 1, in the secondary batteries of Examples 1 to 22 using non-aqueous solvents containing halogenated benzenes and containing less than 100 ppm of amino benzenes, it was found that abnormal heat generation occurred among the ten batteries subjected to the overcharge test. Almost no, at most two (20% or less), the effect of safely terminating the overcharge state is great. In particular, in the secondary batteries of Examples 1 to 4 to which o-CT, p-CT, and o-FT containing an aminoated benzene content of 50 ppm or less are added, the secondary battery of Example 5 having an amino acid content of benzene is 90 ppm. Compared with this, the effect of safely terminating the overcharge state is greater.

On the other hand, in the nonaqueous electrolyte secondary batteries of Comparative Examples 1 to 11 using a nonaqueous solvent containing halogenated benzenes and containing 100 ppm or more of aminoated benzenes, at least three out of ten of them generated abnormal heat generation. .

This invention can be implemented in other various forms, without deviating from the mind or main characteristic. Therefore, the above-described embodiments are merely examples in all respects, and the scope of the present invention is shown in the claims, and is not limited to the specification text at all. Furthermore, all modifications and variations that fall within the scope of the claims are within the scope of the present invention.

The nonaqueous electrolyte and the nonaqueous electrolyte secondary battery of the present invention have an extremely low occurrence rate of abnormal heat generation during overcharge and have a very high safety.

It can be used as a power source that can be used safely in electronic devices such as mobile communication devices, notebook PCs, palmtop PCs, integrated video cameras, portable CD (MD) players, cordless telephones, and the like.

Claims (7)

In a nonaqueous electrolyte containing a nonaqueous solvent and an electrolyte, A nonaqueous electrolyte, wherein the nonaqueous solvent contains halogenated benzenes, and the content of aminated benzenes contained as impurities in the nonaqueous solvent is less than 100 ppm. A nonaqueous electrolyte according to claim 1, wherein the nonaqueous solvent contains carbonates and / or γ-butyrolactone together with halogenated benzenes. The nonaqueous electrolyte according to claim 1 or 2, wherein the halogenated benzenes are at least one selected from halogenated toluene and halogenated xylene having one or two or more chlorine atoms and / or fluorine atoms. The nonaqueous electrolyte according to any one of claims 1 to 3, wherein the halogenated benzenes are at least one selected from o-chlorotoluene, p-chlorotoluene, and o-fluorotoluene. The non-aqueous electrolyte according to any one of claims 1 to 4, wherein the aminated benzenes are at least one selected from aminated toluene and aminated xylene. The non-aqueous electrolyte according to any one of claims 1 to 5, wherein the aminated benzenes are at least one selected from 2-aminotoluene, 4-aminotoluene, and aminoxylene. A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and the nonaqueous electrolyte of any one of claims 1 to 6.

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