JP2002033122A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery having excellent rate characteristics, high energy density and high safety. SOLUTION: The object can be attained by constituting a positive electrode and a negative electrode of transition metal oxide containing lithium and graphite, respectively, including at least ethylene carbonate and γ-butyrolactone in a solvent, using lithium tetrafluoroborate as an electrolyte salt and setting density of the electrolyte salt to >=1.3 mol/l and <=2.3 mol/l.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery, and more particularly to an electrolyte composition for a non-aqueous electrolyte battery.

[0002]

2. Description of the Related Art In recent years, with the great progress in electronic technology, portable devices for general users have been reduced in size and weight.
The demand for smaller and lighter batteries is also increasing. Further, there is a strong demand for a battery having a high energy density.

In the case of non-aqueous electrolyte batteries, as an electrochemically active substance, a substance utilizing intercalation or doping of a layered compound has been particularly studied, and these are expected to have extremely excellent charge / discharge cycle performance. Is done. For example, an example in which graphite is used as an electrochemically active material for a negative electrode has also emerged as a measure to solve problems such as cycle characteristics of the electrochemically active material. This graphite is characterized by a high doping capacity, a low self-discharge rate, excellent cycling properties, and most notably, a base potential very close to lithium metal. That is, in the case of a lithium ion battery as a non-aqueous electrolyte battery that achieves the above-described object,
A lithium-containing transition metal oxide is used for the positive electrode, a carbonaceous material such as graphite is used for the negative electrode, and lithium hexafluorophosphate (LiP) is used for the electrolyte such as ethylene carbonate or the like.
An electrolytic solution in which F ₆ ) is dissolved is used. It is known that LiPF ₆ used in this electrolyte reacts with a trace amount of water present inside the battery to release hydrofluoric acid. Hydrofluoric acid is one of the causative substances that degrade the performance of lithium ion batteries.

On the other hand, lithium tetrafluoroborate (LiBF)
₄ ) is known to hardly react with water, and has the property of stabilizing by combining with water. Therefore, the electrolyte is LiBF
_The use of ₄ can solve the performance deterioration of the battery caused by hydrofluoric acid. This also improves the long-term reliability of the battery.

In general, when graphite is used for the negative electrode,
Solvent compositions based on ethylene carbonate have been proposed. However, when ethylene carbonate is used as a main solvent, a problem occurs in low-temperature characteristics. That is, the melting point of ethylene carbonate is 37 ° C., and the electrolyte solidifies. For the purpose of improving the low-temperature characteristics of a non-aqueous electrolyte secondary battery, Japanese Patent Publication No. 280365 proposes using ethylene carbonate, propylene carbonate, and γ-butyrolactone. However, since LiClO ₄ is used as the lithium salt of the electrolyte, there is a problem in safety. Further, for the purpose of improving the current efficiency of the non-aqueous secondary battery, Japanese Patent Application Laid-Open No. Hei 6-20721 proposes using ethylene carbonate and γ-butyrolactone, and Japanese Patent Application Laid-Open No. Hei 6-52896 discloses ethylene carbonate,
Proposals using propylene carbonate and γ-butyrolactone have been made, and LiBF ₄ having excellent safety is used as the lithium salt of the electrolyte. However, when LiBF ₄ is used as the salt of the electrolytic solution, there has been a problem that, at a salt concentration of 1 mol / l described in the publication, low-temperature characteristics are excellent but high-rate discharge characteristics cannot be sufficiently obtained.

In addition, when a carbonaceous material is used for a negative electrode, the problem that the initial efficiency of the negative electrode is poor has long been known as a phenomenon peculiar to the carbonaceous material. That is, a phenomenon is such that some of the lithium ions stored in the negative electrode by the first charge are consumed for a side reaction. In the case of a lithium ion battery, the amount of lithium ions present in the battery is limited, so the side reaction at the negative electrode has caused the battery capacity to decrease from the beginning.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a non-aqueous electrolyte battery which is excellent in low-temperature performance, safety and high-rate discharge characteristics. The purpose is to: It is another object of the present invention to increase the initial efficiency of the carbonaceous negative electrode and to provide a large capacity nonaqueous electrolyte battery.

[0008]

In order to achieve the above object, a nonaqueous electrolyte battery according to the present invention comprises a positive electrode having a lithium-containing transition metal oxide, a negative electrode having graphite, and a nonaqueous electrolyte comprising a nonaqueous electrolyte. In electrolyte batteries,
The non-aqueous electrolyte contains at least ethylene carbonate and γ-butyrolactone as a solvent, uses lithium tetrafluoroborate as an electrolyte salt, and has a concentration of 1.3.
The first feature is that it is not less than mol / l and not more than 2.3 mol / l.

That is, the present inventors provide a nonaqueous electrolyte battery comprising a positive electrode having a lithium-containing transition metal oxide, a negative electrode having graphite, and a nonaqueous electrolyte.
Surprisingly, by using LiBF ₄ having excellent stability against moisture as the lithium salt of the non-aqueous electrolyte and using a specific solvent, the non-aqueous electrolyte battery having extremely good high-rate discharge characteristics is surprisingly obtained. Was obtained, which led to the present invention.

[0010] Even more surprising is that, as mentioned above, by increasing the salt concentration above that normally used,
The inventors have found that a significant effect of improving the initial efficiency of the carbonaceous negative electrode is obtained, and have reached the present invention.

The solvent ethylene carbonate and γ-
The mixing ratio of butyrolactone is not particularly limited, but when the above-mentioned ethylene carbonate and γ-butyrolactone are respectively 10% by weight or more and 80% by weight or less, excellent battery characteristics can be obtained. Particularly, γ-butyrolactone has an effect of lowering the viscosity of the electrolytic solution. Therefore, when the content is 40% or more, excellent low-temperature characteristics can be obtained.

As the lithium salt used in the nonaqueous electrolyte battery of the present invention, LiBF ₄ having excellent stability to moisture is preferable. In order to further improve low temperature characteristics, LiBF
It is also possible to use a salt other than ₄ in combination. For example, Li
PF ₆ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN
(SO ₂ C ₂ F ₅ ) ₂ and LiC (SO ₂ CF ₃ ) ₃ . The lithium salt concentration of LiBF ₄ is 1.3 to 3.0 m.
ol / l is effective. In particular, it is preferably from 1.7 to 2.3 mol / l. At a salt concentration lower than 1.3 mol / l, a sufficient discharge capacity in a high-rate discharge cannot be obtained. 3.0mo
If the salt concentration is higher than 1 / l, salt is liable to precipitate and the discharge performance deteriorates, which is not preferable.

The second feature of the non-aqueous electrolyte battery of the present invention is that it contains propylene carbonate as a solvent in addition to the ethylene carbonate and γ-butyrolactone.

Although the mixing ratio of these solvents is not particularly limited, ethylene carbonate, γ-butyrolactone and propylene carbonate each contain 10% by weight to 8% by weight.
When the content is 0% by weight or less, excellent battery characteristics can be obtained. In particular, propylene carbonate has a high dielectric constant and can dissolve a high concentration of lithium salt. Therefore, it is preferable to add propylene carbonate in an amount of 10% by weight or more. When the amount of propylene carbonate is 30% by weight or less, decomposition of the electrolytic solution on the negative electrode surface can be suppressed, so that the initial charge / discharge efficiency is improved and a battery having a high energy density is obtained.

Another high dielectric constant solvent may be added to the above-mentioned ethylene carbonate, γ-butyrolactone and propylene carbonate. Preferred examples of the high dielectric constant solvent include cyclic carbonates such as butylene carbonate and vinylene carbonate, and cyclic esters such as valerolactone.

The operation and effect of the present invention are as follows. However, the mechanism of action includes estimation, and its correctness does not limit the present invention. That is, in the non-aqueous electrolyte lithium battery, when discharging, the positive electrode occludes lithium ions and the negative electrode releases lithium ions, so that cations move to the positive electrode and anions move to the negative electrode. Li
When BF ₄ is used, the anion (BF ₄ ⁻ ) is small, and the anion tends to concentrate on the negative electrode. In particular, when high-rate discharge is performed, if the tendency of the anions to concentrate on the negative electrode increases, the number of anions in the vicinity of the positive electrode decreases extremely, making discharge difficult. This is considered to be one of the causes of poor rate characteristics. Therefore, it is considered that by increasing the salt concentration, the extreme polarization of anions is relaxed, and a capacity can be obtained even in a high-rate discharge.

The cause of the poor initial efficiency of the carbonaceous anode is considered to be due to a side reaction in which a part of the solvent not solvated with lithium ions is decomposed on the surface of the carbonaceous anode during the first charge. However, it is considered that by increasing the salt concentration, the proportion of the unsolvated solvent molecules is reduced, so that the side reaction is suppressed.
Furthermore, by increasing the salt concentration, for example, the swelling of the binder used for the electrode such as polyvinylidene fluoride due to the electrolytic solution is also suppressed by the principle of osmotic pressure. It is considered that there is no effect of losing electrical contact, and there is also an effect of suppressing cycle reduction due to repeated charging and discharging. Thereby, a non-aqueous electrolyte battery having a large initial capacity and a large cycle capacity can be provided.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

An electrode composed of a lithium-containing transition metal oxide is preferably used for the positive electrode of the present invention, and an electrode composed of graphite is preferably used for the negative electrode.

As the lithium-containing transition metal oxide for the positive electrode, for example, a lithium-containing transition metal oxide of at least one metal selected from the group consisting of chromium, vanadium, manganese, iron, cobalt and nickel and lithium is used. Is done. Examples of such a lithium-containing transition metal oxide include LiCoO ₂ , LiMn ₂ O ₄ , L
iNiO _{2 and the} like. The general formula Li _y Co _1-x
M _x O ₂ , Li _y Mn _2-x M _x O ₄ (M is a metal of Group I to VIII (for example, Li, Ca, Cr, Ni, Fe, Co
Element), and the x value indicating the replacement amount of the different element is effective up to the maximum amount that can be replaced, but preferably 0 ≦ x ≦ 1 in terms of discharge capacity. For the y value indicating the amount of lithium, the maximum amount capable of reversibly using lithium is effective, and preferably 0 ≦ from the viewpoint of discharge capacity.
y ≦ 2. ) May be used. However, it is not limited to these.

Further, the lithium-containing transition metal oxide is
Other positive electrode active materials may be mixed and used. Other positive electrode active materials
The quality is CuO, Cu_TwoO, Ag_TwoO, CuS, Cu
SO _FourGroup I metal compounds such as TiS_Two, SiO_Two, SnO
Group IV metal compounds such as_TwoO_Five, V₆O₁₂, VO_x, Nb_Two
O_Five, Bi_TwoO_Three, Sb_TwoO_ThreeGroup V metal compound such as Cr
O _Three, Cr_TwoO_Three, MoO_Three, MoS_Two, WO_Three, SeO_Twoetc
Group VI metal compound of MnO_Two, Mn_TwoO_ThreeGroup VII metallization
Compound, Fe_TwoO_Three, FeO, Fe_ThreeO_Four, Ni_TwoO_Three, Ni
O, CoO_ThreeVIII group metal compounds such as, CoO, or
General formula Li_xMX_Two, Li_xMN_yX_Two(M and N are from I to VII
Group I metals, X represents chalcogen compounds such as oxygen and sulfur
Show. ), For example, lithium-cobalt based composite
Metallization of composite oxides and lithium-manganese composite oxides
Compound, furthermore, disulfide, polypyrrole, polyani
Phosphorus, polyparaphenylene, polyacetylene, polyacetylene
Conductive polymer compounds such as carbon-based materials, pseudo-graphite structure
Examples include, but are not limited to, carbonaceous materials.
is not.

For the positive electrode, for example, the lithium-containing transition metal oxide is kneaded with a conductive agent and a binder, and further, if necessary, with a filler to form a positive electrode mixture. Apply or crimp on foil or lath plate, etc.
It is manufactured by performing a heat treatment at a temperature of about 250C to about 2 hours.

Examples of the negative electrode material include graphite capable of inserting and extracting lithium. For example, artificial graphite,
Natural graphite is preferred. In particular, graphite in which the surface of the negative electrode active material particles is modified with amorphous carbon or the like is preferable because gas generation during charging is small. The analysis results of X-ray diffraction and the like of graphite that can be suitably used are shown below: Lattice spacing (d002) 0.333 to 0.350 nm Crystallite size La in the a-axis direction La 20 nm or more c Axial crystallite size Lc 20 nm or more True density 2.00 to 2.25 g / cm ³

It is also possible to modify the graphite by adding a metal oxide such as tin oxide and silicon oxide, phosphorus, boron, amorphous carbon and the like to graphite. In particular, by modifying the surface of graphite by the above-described method, it is possible to suppress the decomposition of the electrolyte and to improve the battery characteristics, which is desirable. Furthermore, for graphite,
Lithium metal, lithium-aluminum, lithium-
Lead, lithium-tin, lithium-aluminum-tin,
Lithium metal-containing alloys such as lithium-gallium and wood alloys can be used together, and graphite into which lithium has been inserted by electrochemical reduction in advance can also be used as the negative electrode active material.

The negative electrode is prepared, for example, by kneading the above graphite with a binder, and, if necessary, a conductive agent, a thickener or a filler to form a negative electrode mixture, and then using the negative electrode mixture as a foil as a current collector. 50 ° C ~ 250
It is produced by heat treatment at a temperature of about 2 ° C. for about 2 hours.

It is also possible to modify at least the surface layer portion of the powder of the positive electrode active material and the powder of the negative electrode active material with a material having good electron conductivity and ion conductivity, or a compound having a hydrophobic group. For example, materials having good electron conductivity such as gold, silver, carbon, nickel, and copper, lithium carbonate,
A material having good ion conductivity, such as boron glass or a solid electrolyte, or a material having a hydrophobic group such as silicone oil is coated by applying a technique such as plating, sintering, mechanofusion, vapor deposition, or baking.

The powder of the positive electrode active material and the powder of the negative electrode active material preferably have an average particle size of 100 μm or less. In particular, the powder of the positive electrode active material is desirably 10 μm or less for the purpose of improving the high output characteristics of the nonaqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, mortar, ball mill, sand mill,
A vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air jet mill, a sieve, and the like are used. At the time of pulverization, wet pulverization in which an organic solvent such as water or hexane coexists can be used. There are no particular limitations on the classification method, such as a sieve or a wind classifier,
Both dry and wet types are used as needed.

The conductive agent is not limited as long as it is an electron conductive material which does not adversely affect the battery performance, and is usually natural graphite (scale graphite, flake graphite, earth graphite, etc.),
One or more conductive materials such as artificial graphite, carbon black, acetylene black, Ketjen black, carbon whiskers, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material They can be included as a mixture thereof.

Among these, acetylene black is preferred as the conductive agent from the viewpoints of conductivity and coatability. The amount of the conductive agent to be added is preferably 1% by weight to 50% by weight, more preferably 2% by weight to 30% by weight based on the total weight of the positive electrode or the negative electrode. These mixing methods are physical mixing, and ideally, uniform mixing. Therefore, V-type mixer, S-type mixer, grinder, ball mill,
It is possible to mix a powder mixer such as a planetary ball mill in a dry or wet manner.

Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, and polypropylene; ethylene-propylene diene terpolymer (EPDM); Polymers having rubber elasticity such as styrene butadiene rubber (SBR) and fluoro rubber can be used as one kind or as a mixture of two or more kinds. The addition amount of the binder is preferably 1 to 50% by weight, and particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

As the thickener, polysaccharides such as carboxymethylcellulose, methylcellulose and the like can be usually used as one kind or as a mixture of two or more kinds. Further, it is desirable that a binder having a functional group that reacts with lithium, such as a polysaccharide, be deactivated by, for example, methylation. The addition amount of the thickener is preferably 0.5 to 10% by weight, and particularly preferably 1 to 2% by weight, based on the total weight of the positive electrode or the negative electrode.

The filler may be any material as long as it does not adversely affect battery performance. Usually, olefin polymers such as polypropylene and polyethylene, aerosil, zeolite, glass, carbon and the like are used. The amount of the filler is preferably 30% by weight or less based on the total weight of the positive electrode or the negative electrode.

For the positive electrode and the negative electrode, the active material, the conductive agent and the binder are mixed with an organic solvent such as N-methylpyrrolidone and toluene, or purified water, and the resulting mixed solution is described in detail below. It is suitably prepared by applying it on a current collector and drying it. For the coating method, for example, roller coating such as an applicator roll, screen coating, doctor blade method,
It is desirable to apply to an arbitrary thickness and an arbitrary shape using a means such as spin coating and a bar coder, but it is not limited thereto.

The current collector may be any electronic conductor that does not adversely affect the battery structure. For example, as the positive electrode current collector, aluminum, titanium,
In addition to stainless steel, nickel, calcined carbon, conductive polymer, conductive glass, etc., the surface of aluminum, copper, etc. is coated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesion, conductivity and oxidation resistance. Can be used. As the current collector for the negative electrode, copper, nickel, iron, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc.
For the purpose of improving conductivity and oxidation resistance, a material obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver, or the like can be used. These materials can be oxidized on the surface.

Regarding the shape of the current collector, in addition to a foil shape, a film shape, a sheet shape, a net shape, a punched or expanded material, a lath body, a porous body, a foamed body, a fiber group formed body, and the like are used. Can be There is no particular limitation on the thickness.
〜500 μm is used. Among these current collectors, as the positive electrode, aluminum foil having excellent oxidation resistance is used, and as the negative electrode, copper foil, nickel foil, iron, which is stable in the reduction field and has excellent electrical conductivity, and is inexpensive. It is preferred to use foils, and alloy foils containing some of them.
Further, it is preferable that the foil has a rough surface roughness of 0.2 μm Ra or more, whereby the adhesion between the positive electrode active material or the negative electrode active material and the current collector becomes excellent. Therefore, it is preferable to use an electrolytic foil because of having such a rough surface. In particular, an electrolytic foil subjected to a napping treatment is most preferable.

As the separator used in the nonaqueous electrolyte battery of the present invention, a nonwoven fabric, a porous membrane, or the like can be used. As a material constituting the separator, polyethylene,
Examples thereof include polyolefins represented by polypropylene, polyesters represented by polyethylene terephthalate and polybutylene terephthalate, polyphenylene sulphite, polyimide, polyacrylonitrile, polymethyl methacrylate, polyethylene oxide, and fluorine resin. Above all, a polypropylene porous membrane which can be expected to have a shutdown effect is desirable. The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength.
Further, the porosity is preferably 20% by volume or more from the viewpoint of charge and discharge characteristics.

As the separator, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, etc. and an electrolyte may be used.

Further, the separator for a non-aqueous electrolyte battery is
It is preferable to use a polymer gel in combination with the above-described porous membrane, nonwoven fabric, or the like, since the liquid retention of the electrolytic solution is improved.
That is, by forming a film coated with a lipophilic polymer having a thickness of several μm or less on the surface of the polyethylene microporous membrane and the microporous wall surface, and by holding the electrolytic solution in the micropores of the film,
It can be a polymer gel.

Examples of the solvent-philic polymer include a polyvinylidene fluoride monomer, an acrylate monomer having an ethylene oxide group and an ester group, an epoxy monomer, and the like.
For example, a polymer in which a monomer having an isocyanate group is crosslinked. The cross-linking reaction can be performed using actinic rays such as ultraviolet rays (UV) and electron beams (EB).

For the purpose of controlling the strength and the physical properties, the solvent-philic polymer can be used by blending a physical property modifier within a range that does not hinder the formation of the crosslinked product. Examples of the physical property modifier include inorganic fillers {metal oxides such as silicon oxide, titanium oxide, aluminum oxide, magnesium oxide, zirconium oxide, zinc oxide and iron oxide, and metal carbonates such as calcium carbonate and magnesium carbonate}. And polymers {polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, and the like}. The amount of the physical property modifier is usually 50% by weight or less, preferably 20% by weight or less, based on the crosslinkable monomer.

As an example of the acrylate monomer, a bifunctional or higher functional unsaturated monomer is preferably exemplified.
More specific examples include bifunctional (meth) acrylate ｛ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, adipic acid / dineopentyl glycol ester di (meth) acrylate, and polyethylene glycol having a degree of polymerization of 2 or more. Di (meth) acrylate, polypropylene glycol di (meth) acrylate having a degree of polymerization of 2 or more, di (meth) acrylate of polyoxyethylene / polyoxypropylene copolymer, butanediol di (meth) acrylate, hexamethylene glycol di (meth) acrylate ) Acrylate, etc., trifunctional (meth)
Acrylate: trimethylolpropane tri (meth) acrylate, glycerin tri (meth) acrylate, tri (meth) acrylate of glycerin ethylene oxide adduct, tri (meth) acrylate of glycerin propylene oxide adduct, glycerin ethylene oxide, propylene oxide addition Tri (meth) acrylate, etc.}, polyfunctional (meth) acrylate having 4 or more functional groups, pentaerythritol tetra (meth) acrylate,
And diglycerin hexa (meth) acrylate. These monomers can be used alone or in combination.

A monofunctional monomer may be added to the acrylate monomer for the purpose of adjusting physical properties and the like. Examples of the monofunctional monomer include unsaturated carboxylic acids ｛acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, vinylbenzoic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, methylenemalonic acid, Aconitic acid, etc., unsaturated sulfonic acid {styrene sulfonic acid, acrylamide-2-methylpropane sulfonic acid, etc.} or a salt thereof (Li salt, Na salt, K salt, ammonium salt,
Tetraalkylammonium salts, etc.) and also partially esterify these unsaturated carboxylic acids with C1-C18 aliphatic or alicyclic alcohols, alkylene (C2-C4) glycols, polyalkylene (C2-C4) glycols, etc. (Methylmalate, monohydroxyethylmalate, etc.) and partially amidated with ammonia and primary or secondary amines (maleic acid monoamide, N-methylmaleic acid monoamide, N, N-diethylmaleic acid) Monoamide), (meth) acrylic acid ester [C1-C18 aliphatic (methyl, ethyl, propyl, butyl, 2-ethylhexyl, stearyl, etc.)
Ester of alcohol and (meth) acrylic acid, or alkylene (C2-C4) glycol (ethylene glycol, propylene glycol, 1,4-butanediol, etc.) and polyalkylene (C2-C4) glycol (polyethylene glycol, polypropylene glycol) With (meth) acrylamide or N-substituted (meth) acrylamide [(meth) acrylamide, N-methyl (meth) acrylamide, N-methylol (meth) acrylamide, etc.]; vinyl ester or Allyl ester [vinyl acetate, allyl acetate, etc.]; vinyl ether or allyl ether [butyl vinyl ether, dodecyl allyl ether, etc.]; unsaturated nitrile compound [(meth) acrylonitrile, crotonnitrile, etc.]; Saturated alcohols [(meth) allyl alcohol]; unsaturated amines [(meth) allylamine, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate];
Heterocycle-containing monomer [N-vinylpyrrolidone, vinylpyridine, etc.]; olefinic aliphatic hydrocarbon [ethylene,
Propylene, butylene, isobutylene, pentene, (C
6-C50) α-olefins, etc.]; olefin-based alicyclic hydrocarbons [cyclopentene, cyclohexene, cycloheptene, norbornene, etc.]; olefin-based aromatic hydrocarbons [styrene, α-methylstyrene, stilbene, etc.];
Unsaturated imide [maleimide etc.]; halogen-containing monomer [vinyl chloride, vinylidene chloride, vinylidene fluoride, hexafluoropropylene etc.] and the like.

Examples of the epoxy monomer include glycidyl ethers such as bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, brominated bisphenol A diglycidyl ether, phenol novolac glycidyl ether, cresol novolac glycidyl ether, and glycidyl esters. Glycidyl hexahydrophthalate, glycidyl dimer, etc.｝, glycidylamines ｛triglycidyl isocyanurate, tetraglycidyldiaminophenylmethane, etc.｝, linear aliphatic epoxides ｛epoxidized polybutadiene, epoxidized soybean oil, etc.｝,
Alicyclic epoxides {3,4 epoxy-6 methylcyclohexylmethyl carboxylate, 3,4 epoxy cyclohexylmethyl carboxylate, etc.}; These epoxy resins can be used alone or after being cured by adding a curing agent.

Examples of the curing agent include aliphatic polyamines such as diethylene triamine, triethylene tetramine,
3,9- (3-aminopropyl) -2,4,8,10-
Tetrooxaspiro [5,5] undecane, etc., aromatic polyamines, such as meta-xylene diamine, diaminophenylmethane, etc., polyamides, such as dimer acid polyamide, etc., acid anhydrides, phthalic anhydride, tetrahydromethyl phthalic anhydride. , Hexahydrophthalic anhydride, trimellitic anhydride, methylnadic anhydride, phenols such as phenol novolak, polymercaptans such as polysulfide, tertiary amines tris (dimethylaminomethyl) phenol, 2-ethyl-4 -Methylimidazole, etc.}, Lewis acid complex {boron trifluoride / ethylamine complex, etc.} and the like.

Examples of the monomer having an isocyanate group include toluene diisocyanate, diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4 (2,2,4) -trimethyl-hexamethylene diisocyanate, and p-phenylene diisocyanate. 4,4′-dicyclohexylmethane diisocyanate, 3,3′-dimethyldiphenyl 4,4′-diisocyanate, dianisidine diisocyanate, m-xylene diisocyanate, trimethyl xylene diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, trans
-1,4-cyclohexyl diisocyanate, lysine diisocyanate and the like.

In crosslinking the monomer having an isocyanate group, polyols and polyamines [bifunctional compounds {water, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol and the like], trifunctional compounds {glycerin, trimethylolpropane, 1,4,6-hexanetriol, triethanolamine, etc., tetrafunctional compound, pentaerythritol, ethylenediamine, tolylenediamine, diphenylmethanediamine, tetramethylolcyclohexane,
Methyl glucoside, etc.｝ pentafunctional compound ｛2,2,6,6
-Tetrakis (hydroxymethyl) cyclohexanol, diethylenetriamine and the like {, 6-functional compound {sorbitol, mannitol, dulcitol, etc.}, 8-functional compound {sucrose, etc.}], and polyether polyols {propylene oxide and / or the polyol or polyamine) An ethylene oxide adduct {, a polyester polyol [condensation product of the polyol and a polybasic acid {adipic acid, o, m, p-phthalic acid, succinic acid, azelaic acid, sebacic acid, ricinoleic acid};
Compounds having active hydrogen can be used in combination, such as polycaprolactone polyol {poly-ε-caprolactone, etc.}, polycondensates of hydroxycarboxylic acids, etc.].

In the crosslinking reaction, a catalyst can be used in combination. Examples of the catalyst include organotin compounds, trialkylphosphines, amines [monoamines {N, N-dimethylcyclohexylamine, triethylamine, etc.}, cyclic monoamines {pyridine, N-methylmorpholine, etc.}, diamines} N, N, N ', N'
-Tetramethylethylenediamine, N, N, N ', N'
-Tetramethyl 1,3-butanediamine etc., triamines {N, N, N ', N'-pentamethyldiethylenetriamine etc.}, hexamines {N, N, N'N'-tetra (3-dimethylaminopropyl) ) -Methanediamine, etc., cyclic polyamines, diazabicyclooctane (D
ABCO), N, N'-dimethylpiperazine, 1,2-
Dimethylimidazole, 1,8-diazabicyclo (5,
4,0) undecene-7 (DBU) and the like, and salts thereof.

It is preferable to use the non-aqueous electrolyte of the present invention in a gel state as described above, particularly since the electrolyte composition of the present invention has a high salt concentration and has an effect of suppressing the precipitation of salts.

The configuration of the nonaqueous electrolyte battery is not particularly limited, and coin batteries and button batteries having a positive electrode, a negative electrode and a single-layer or multiple-layer separator,
Examples include a cylindrical battery, a prismatic battery, and a flat battery having a positive electrode, a negative electrode, and a roll-shaped separator.

As the material of the exterior body of the nonaqueous electrolyte battery,
Examples include nickel-plated iron, stainless steel, aluminum, and metal resin composite films. For example, a metal-resin composite film having a configuration in which a metal foil is sandwiched between resin films is preferable. Specific examples of the metal foil include, but are not limited to, aluminum, iron, nickel, copper, stainless steel, titanium, gold, silver, and the like, as long as they have no pinholes. Preferably, a lightweight and inexpensive aluminum foil is preferable. As the resin film on the outside of the battery, a resin film having excellent piercing strength such as a polyethylene terephthalate film or a nylon film can be used, and as the resin film on the inside of the battery, a polyethylene film or a nylon film can be used. It is preferable to use a film that has a solvent resistance.

[0051]

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, which do not limit the present invention at all.

(Battery 1 of the Invention) [Preparation of Electrolyte A] 70% by weight of γ-butyrolactone and 30% by weight of ethylene carbonate were mixed, and Li was added thereto.
BF ₄ was dissolved to a concentration of 2.0 mol / l to prepare electrolyte solution A.

[Preparation of electrolyte solution B] 30% by weight of propylene carbonate, 50% by weight of γ-butyrolactone and 20% by weight of ethylene carbonate were mixed, and LiBF was added thereto.
₄ was dissolved to a concentration of 2.0 mol / l to prepare an electrolytic solution B.

[Production of Nonaqueous Electrolyte Battery] LiCoO
₂ (Positive electrode active material) 90% by weight, acetylene black (conductive agent) 5% by weight and polyvinylidene fluoride (binder) 5
% By weight and kneaded with N-methylpyrrolidone. The obtained paste was applied on an aluminum foil, dried and pressed to produce a positive electrode. A positive electrode terminal was welded to the positive electrode by ultrasonic welding.

97% by weight of artificial graphite (negative electrode material), 2% by weight of styrene butadiene rubber (binder) and 1% by weight of carboxymethyl cellulose (thickener) were mixed and kneaded with purified water. Apply the obtained paste on copper foil,
After drying and pressing, a negative electrode was prepared. The negative electrode terminal was welded to the negative electrode by resistance welding.

A separator was formed by using a polypropylene microporous membrane surface-modified with polyacrylate to improve the retention of the electrolytic solution as a separator, laminated in the order of negative electrode / separator / positive electrode and wound into a flat shape to obtain an electrode group. .

A metal resin composite film composed of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal adhesive polypropylene film (50 μm) is used as the outer package, and the open ends of the positive electrode terminal and the negative electrode terminal are exposed outside. As described above, airtight sealing was performed except for the portion that became a liquid injection hole.

After injecting a certain amount of the electrolytic solution 1 from the injection hole, the injection hole portion was heat-sealed in a vacuum state to obtain a design capacity of 5.
A flat non-aqueous electrolyte battery of 00 mAh was produced, and was designated as Battery 1 of the invention.

(Batteries 2 to 4 of the Present Invention) L used for electrolytic solution A
iBF ₄ concentrations of 2.3 mol / l, 1.7 mol / l,
A non-aqueous electrolyte battery was prepared in the same manner as the battery 1 of the present invention, except that the concentration was 1.3 mol / l. The battery 2 of the present invention, the battery 3 of the present invention, and the battery 4 of the present invention were obtained, respectively.

(Comparative batteries 1 and 2) Li used for electrolyte solution A
A non-aqueous electrolyte battery was produced in the same manner as the battery 1 of the present invention except that the BF ₄ concentration was set to 1.0 mol / l and 0.6 mol / l, respectively.

A battery was also prepared with a LiBF ₄ concentration of 2.5 mol / l used for the electrolyte solution A, but salt (LiBF ₄ ) precipitation was observed during the standing of the adjusted electrolyte solution. The production of the battery was stopped.

(Batteries 5 to 8 of the Present Invention) Batteries were prepared in the same manner as Battery A of the present invention, except that Electrolyte B was used instead of Electrolyte A. Further, electrolyte B
The concentration of LiBF ₄ used for the reaction was 2.3 mol / l and 1.7, respectively.
A non-aqueous electrolyte battery was prepared in the same manner as the battery 5 of the present invention except that the mol / l and 1.3 mol / l were used, and the battery 6 of the present invention, the battery 7 of the present invention, and the battery 8 of the present invention were obtained, respectively.

(Comparative batteries 3 and 4) Li used for electrolyte B
A non-aqueous electrolyte battery was prepared in the same manner as the battery 5 of the present invention, except that the BF ₄ concentration was set to 1.0 mol / l and 0.6 mol / l, respectively.

A battery was also prepared in which the concentration of LiBF ₄ used for the electrolyte B was 2.5 mol / l. However, precipitation of salt (LiBF ₄ ) was observed during the standing of the adjusted electrolyte. The production of the battery was stopped. [Measurement of battery characteristics] Batteries 1 to 8 of the present invention and comparative batteries 1 to
4.1 at room temperature (25 ° C.)
After the constant current and constant voltage charging of 0 mA and 7 hours, 100
A low current discharge of mA and a final voltage of 2.7 V was performed. Then, 500m while sandwiching the low current and low voltage charging under the same conditions
A, a discharge test at 1000 mA and 1500 mA was performed. The discharge capacity at 100 mA was defined as 100%, and the capacity ratio at each current density was calculated. The results are shown in Tables 1 and 2. Next, the results obtained by plotting these results in relation to the salt concentration are shown in FIGS. 1 and 2, respectively.

[0065]

[Table 1]

[0066]

[Table 2] [Confirmation of Initial Efficiency Improvement Effect] Next, the monoelectrode cell of the carbonaceous negative electrode was assembled, and the effect of the electrolytic solution composition of the present invention using a salt concentration higher than normally used on the initial efficiency of the carbonaceous negative electrode was shown. confirmed.

Propylene carbonate 30% by weight, γ-
Butyrolactone 40% by weight and ethylene carbonate 3
0% by weight, and LiBF ₄ was added thereto in an amount of 0.6 to 2.3 m.
An ol / l concentration was dissolved to prepare an electrolytic solution, which was used. Example 1 was the same as Example 1 except that a nickel plate to which metal lithium was stuck instead of the positive electrode of Example 1 was arranged as a counter electrode, and a nickel wire with a small amount of metal lithium attached to the tip was arranged as a reference electrode on the separator. A battery was similarly assembled.

While monitoring the potential of the carbonaceous negative electrode based on the potential of the reference electrode, the potential of the
V, the doping / de-doping was performed on the carbonaceous electrode at a current of 500 mA so as to change in the range of 0 V. The first dedope electricity amount with respect to the initially doped electricity amount was defined as the initial efficiency (%). Table 3 shows the effect of the salt concentration on the initial efficiency.

[0069]

[Table 3] As is clear from the above results, the salt concentration was 1.3 mol / l.
The battery of the present invention described above exhibited better high-rate discharge characteristics than the comparative battery in which the salt concentration was 1.0 mol / l or less.
In particular, in a high-rate discharge of 1500 mA (20 fraction), a critical effect was recognized as compared with a comparative battery having a salt concentration of 1.0 mol / l or less. It was also found that the higher the salt concentration, the higher the initial efficiency of the carbonaceous negative electrode. As described above, when the salt concentration is 2.5 mol / l or more, salt precipitation occurs, which is not preferable.

[0070]

As described above, according to the present invention, the solvent contains at least ethylene carbonate and γ-butyrolactone, lithium tetrafluoroborate is used as the electrolyte salt, and the concentration of the electrolyte salt is 1.3 mol / mol. Since the non-aqueous electrolyte battery excellent in high-rate discharge characteristics can be provided by setting the amount to 1 mol or more and 2.3 mol / l or less, the industrial value is extremely large.
Further, since the higher the salt concentration, the more effective the initial efficiency of the carbonaceous negative electrode is, it is possible to provide a large amount of nonaqueous electrolyte battery.

[Brief description of the drawings]

FIG. 1 is a graph showing a discharge capacity at each discharge current in relation to a salt concentration.

FIG. 2 is a graph showing a discharge capacity at each discharge current in relation to a salt concentration.

Claims (2)

[Claims] 1. A non-aqueous electrolyte battery comprising a positive electrode having a lithium-containing transition metal oxide, a negative electrode having graphite, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains at least ethylene carbonate and γ-butyrolactone as a solvent. Lithium tetrafluoroborate is used as an electrolyte salt, and the concentration of the electrolyte salt is at least 1.3 mol / l.
A non-aqueous electrolyte battery characterized by being at most 3 mol / l. 2. The non-aqueous electrolyte battery according to claim 1, wherein the non-aqueous electrolyte further includes propylene carbonate as a solvent.