JP2003100294A - Negative active material for battery and non-aqueous electrolyte battery using the same - Google Patents

Abstract

[PROBLEMS] To provide a negative electrode active material for a battery having high energy density, excellent cycle characteristics, rate characteristics and low-temperature performance, and a non-aqueous electrolyte battery using the same. SOLUTION: A negative electrode active material for a battery is used in which a carbonaceous material A comprising graphite containing 15% or more of a rhombohedral structure is coated with a carbonaceous material B not containing a rhombohedral structure. Thus, the above problem can be solved. The carbonaceous material A preferably has a crystallite size Lc of 100 nm or more, and the negative electrode active material for a battery preferably has a specific surface area of 3 m ² / g or less according to a BET method. The non-aqueous electrolyte battery used preferably contains a carbonate having a double bond, and further contains propylene carbonate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a negative electrode active material active material for a battery and a non-aqueous electrolyte battery using the same.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte batteries, especially lithium ion secondary batteries, have been used in mobile phones, PHS (simple mobile phones),
It is drawing attention as a power source for portable devices such as small computers, a power source for power storage, and a power source for electric vehicles. The lithium-ion secondary battery has a problem that the discharge performance at low temperatures is not sufficient, and there has been a strong demand for a lithium secondary battery that exhibits good low-temperature performance. There has also been a demand for batteries that are small, lightweight, and have high energy density.

A lithium ion secondary battery is generally composed of a positive electrode having a positive electrode active material as a main constituent, a negative electrode having a negative electrode active material as a main constituent, and a non-aqueous electrolyte. Examples of the positive electrode active material include lithium-containing transition metal oxides,
The negative electrode active material is a carbonaceous material typified by graphite having a hexagonal crystal structure, and the non-aqueous electrolyte is an electrolyte salt such as lithium hexafluorophosphate (LiPF ₆ ) and a non-aqueous solvent such as ethylene carbonate. Those dissolved in are widely used.

However, since ethylene carbonate, which is an electrolyte solvent, has a high melting point and the electrolytic solution is likely to coagulate at low temperatures, it has been a cause of poor lithium-ion secondary battery low-temperature performance. Therefore, in place of ethylene carbonate, a method of using propylene carbonate having a lower melting point as a non-aqueous solvent of the electrolytic solution is known, but particularly when graphite having a high graphitization rate is used as the negative electrode active material, during charging. Since the side reaction such as the decomposition of propylene carbonate on the graphite negative electrode is large, the irreversible capacity is large, which causes the battery performance to be greatly reduced.

As a means for solving this problem, Japanese Unexamined Patent Publication No.
0-97870 discloses a trial in which graphite having a rhombohedral system structure is used as a negative electrode active material to suppress delamination and reduce irreversible capacity in a battery system using a propylene carbonate-containing electrolytic solution. Has been done. Also,
Simon, B; Flandrois.S; Fevrier-Bouvier, A; Biensan, P.He
xagonal vs Rhombohedral Graphite: The Effect of C
rystal Structure on the Electrochemical Intercalat
ion on Lithium Ion.Mol.Cryst.Liq.Cryst.vol.310,199
In addition to the above effects, 8, p.333-340. Describes a method of obtaining a carbonaceous material containing a rhombohedral structure in graphite at an arbitrary ratio of several% to several tens%.

Further, in Japanese Unexamined Patent Publication No. 11-111297, it is necessary to prevent the crystal structure of graphite from having more than 30% of crystals having a rhombohedral crystal structure in order to prevent decomposition of the electrolytic solution. It is stated that there is. Also,
As a solvent used for the electrolytic solution, ethylene carbonate as a first solvent and a solvent generally known as a second solvent, for example, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DE
Carbonates having no double bond such as C) and propylene carbonate (PC) are mentioned.

On the other hand, Japanese Patent Application Laid-Open No. 11-283667 discloses that vinylene carbonate is used in combination with graphite-based carbonaceous material as a negative electrode active material because it does not cause decomposition of propylene carbonate. . Also,
It is described that the addition amount of vinylene carbonate is required to be 5% or more. This is because if the amount of vinylene carbonate added is less than 5%, the battery capacity will be reduced.

[0008] Further, Japanese Patent No. 3106129 and Japanese Patent No. 3139790 disclose that the carbonaceous material constituting the nucleus is related to the surface modification of the carbonaceous material.
Further, a secondary battery having a large electrode capacity and improved cycle characteristics has been proposed by using a carbonaceous material having a surface layer of a carbonaceous material formed thereon.

However, in any of the reports, there is a problem that the negative electrode active material cannot exhibit 100% of its inherent performance with respect to low temperature performance, charge / discharge efficiency characteristics and cycle characteristics in a lithium battery, and an electrode plate using a carbonaceous material. There was a problem in that it was difficult to make.

[0010]

The present invention has been made in view of the above problems and has a high energy density,
An object of the present invention is to provide a negative electrode active material for a battery, which is excellent in cycle characteristics, rate characteristics, and low-temperature performance, and a non-aqueous electrolyte battery using the same.

[0011]

In order to solve the above problems, as a result of intensive studies, the present inventors have found that graphite having a rhombohedral system structure is replaced with a carbonaceous material having no rhombohedral system structure. By coating, using a carbonaceous material with a large crystal lattice size and a small specific surface area for the negative electrode, and further specifying a non-aqueous solvent that constitutes the non-aqueous electrolyte, surprisingly high energy density and excellent The inventors have found that a non-aqueous electrolyte battery having both cycle characteristics, rate characteristics, and low-temperature performance can be obtained, and completed the present invention. That is, the technical configuration of the present invention and its effects are as follows. However, the mechanism of action includes estimation, and its correctness does not limit the present invention.

That is, according to the present invention, as described in claim 1, the surface of the carbonaceous material A made of graphite containing 15% or more of the rhombohedral crystal structure does not contain a rhombohedral crystal structure. A negative electrode active material for a battery, which is coated with a material B.

That is, the most general structure of graphite is a hexagonal structure, and the carbon network plane has an ABAB type laminated structure in which the B layer close to the A layer is displaced. On the other hand, as another thermodynamically metastable state, there is a rhombohedral crystal structure, which is an ABCABC type laminated structure. Most graphite crystals and artificial graphite have a hexagonal crystal structure, but it is recognized that natural graphite and artificial graphite heat-treated at a very high temperature contain a rhombohedral crystal structure. In addition, it has been reported that pulverization and grinding cause a structural change from a hexagonal crystal structure to a rhombohedral crystal structure.
When graphite having a hexagonal structure is used as the negative electrode and propylene carbonate is used as the solvent of the electrolyte, the SEI (Solid Electrolyte Interface) layer formed when the lithium ions are electrochemically intercalated is sufficient. It was not formed, and as a result, the irreversible capacity was large and the battery performance was not good.

On the other hand, the carbonaceous material obtained by coating the surface of the carbonaceous material A made of graphite containing 15% or more of the rhombohedral crystal structure with the carbonaceous material B not containing the rhombohedral crystal structure is used for the battery. By using it for the negative electrode, surprisingly,
It was found that it has an effect of greatly reducing the irreversible capacity of the battery.

Further, according to the present invention, as described in claim 2, the carbonaceous material A has Lc showing a crystallite size of 100 nm or more, and the battery negative electrode active material is BE.
The negative electrode active material for batteries has a specific surface area of 3 m ² / g or less as measured by the T method.

That is, since the crystallite size (Lc) is proportional to the number of carbon atom planes arranged in parallel, the theoretical capacity of graphite (372) is obtained when Lc is 100 nm or more.
It is possible to obtain a capacity close to mAh / g). Further, since the specific surface area of the battery negative electrode active material is 3 m ² / g or less, it is possible to reduce the amount of the binder at the time of producing the negative electrode plate of the battery, and improve cycle characteristics and rate performance. To do. Furthermore, the coatability is improved, and the value as a negative electrode active material in the production of electrode plates is high.

Further, according to the present invention, as described in claim 3, a negative electrode produced by using the negative electrode active material for a battery, a positive electrode, and a non-aqueous electrolyte containing a carbonate having a double bond are used. The non-aqueous electrolyte battery is manufactured by the following method.

That is, the carbonaceous material A made of graphite containing a rhombohedral crystal structure, particularly graphite containing 15% or more of the rhombohedral crystal structure, has a carbonaceous material B containing no rhombohedral structure on the surface.
It was found that, when graphite having a double bond was combined as a solvent of an electrolyte when graphite coated with was used as a negative electrode, it was surprisingly effective in greatly reducing the irreversible capacity. This effect was recognized as a specific phenomenon when a carbonate having a double bond was used. A carbonate having a double bond is susceptible to reduction, and in particular, a protective film (SEI) is selectively formed on the surface of an active carbonaceous material having a rhombohedral structure, which prevents reductive decomposition of other solvents. It is considered that there is an effect of greatly reducing the irreversible capacity. Further, since the surface of graphite is covered with a carbonaceous material that does not contain a rhombohedral system structure, it is considered that a part of the active sites is covered and deactivated, which makes the effect remarkable.

The present invention also provides a non-aqueous electrolyte battery in which the non-aqueous electrolyte contains at least propylene carbonate.

As described above, the carbonaceous material A made of graphite containing a rhombohedral crystal structure, particularly graphite containing 15% or more of the rhombohedral crystal structure, does not contain a rhombohedral crystal structure on the surface of the carbonaceous material A. The effect when the negative electrode active material coated with the material B is used for the negative electrode is particularly remarkable when propylene carbonate is used as the solvent of the non-aqueous electrolyte. Since propylene carbonate has a low viscosity and an excellent dielectric constant, ionic conduction can be ensured even at a low temperature without increasing the viscosity of the electrolytic solution. Further, by using graphite containing a rhombohedral structure, particularly graphite containing 15% or more of a rhombohedral structure and coated with a carbonaceous material not containing a rhombohedral structure, the above-mentioned double bond can be eliminated. By the action of the carbonate contained therein, the decomposition of propylene carbonate on the negative electrode during charging can be surely suppressed, so that charging can be sufficiently performed. Therefore,
A non-aqueous electrolyte battery having both high energy density, excellent cycle characteristics, rate characteristics, and low-temperature performance can be obtained.

Even more surprisingly, when a carbonate having a double bond and a propylene carbonate are used in combination, even if the electrolyte solvent contains 80% by volume of propylene carbonate, extreme decomposition of the electrolytic solution is caused. It was found that the above-mentioned remarkable effects were exhibited without causing this.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the present invention will be described below, but the present invention is not limited to the following examples.

In the negative electrode active material for a battery of the present invention, the surface of the carbonaceous material A made of graphite containing 15% or more of the rhombohedral crystal structure is coated with the carbonaceous material B not containing the rhombohedral crystal structure. It becomes. As the graphite containing 15% or more of the rhombohedral structure, for example, (002) according to the X-ray diffraction method is used.
The surface spacing (d ₀₀₂ ) of the surfaces is 0.3354 to 0.338 nm
And the crystallite size (Lc) in the c-axis direction is 20 nm.
Carbonaceous materials having a high degree of graphitization such as the above-mentioned natural graphite, quiche graphite, and artificial graphite are preferable. In particular, the content ratio of the rhombohedral structure is preferably 18% or more, more preferably 2
It is 0% or more, more preferably 22% or more, particularly preferably 24% or more, and most preferably 25% or more. Among them, graphite having Lc of 100 nm or more is preferable because it is possible to obtain a capacity close to the theoretical capacity of graphite (372 mAh / g).

The carbonaceous material B coated on the surface of graphite containing 15% or more of a rhombohedral structure is obtained by heating an organic compound under an inert gas flow to decompose and carbonize it. preferable. Here, the carbonaceous material B is not particularly limited as long as it does not include a carbonaceous material having a rhombohedral crystal structure. Examples of the crystal system that the carbonaceous material B can have include a cubic system, a hexagonal system, and an amorphous system, but are not limited thereto. Regarding the crystallinity of the carbonaceous material B, it may be a crystalline carbonaceous material or an amorphous carbonaceous material,
A crystalline carbonaceous material is preferable in order to increase the storage amount of lithium. However, in order to sufficiently exert the effects of the present invention such as preventing the electrolytic solvent such as propylene carbonate from decomposing during charging, it is preferable to use a low crystalline carbonaceous material or an amorphous carbonaceous material. . Further, it may be a mixture of two or more kinds of crystalline carbonaceous material, low crystalline carbonaceous material or non-crystalline carbonaceous material.

As a method of forming the carbonaceous material B on the surface of the carbonaceous material A, the following method is exemplified and can be arbitrarily selected.

(I) The surface of the carbonaceous material A is coated with an organic polymer compound and pyrolyzed in the solid phase to form the carbonaceous material B. Examples of the organic polymer compound include polyvinyl alcohols; celluloses typified by carboxymethyl cellulose; phenol resins; acrylic resins such as polyacrylonitrile and poly (α-halogenated acrylonitrile); polyamideimide resins; polyamide resins; Can be used. Among these, water-soluble polyvinyl alcohol and celluloses are preferable because they are excellent in workability.

(II) Carbonaceous material B obtained by vapor-phase pyrolysis of a relatively low-molecular organic compound or pyrolysis of fog droplets.
Are generated and deposited on the surface of the carbonaceous material A. The relatively low molecular weight organic compound has, for example, 20 carbon atoms.
And paraffins, olefins, aromatic compounds, etc. to a certain degree or less, and more specifically, saturated or unsaturated aliphatic hydrocarbons represented by propane, propylene, etc .; aromatic monocyclic hydrocarbons such as benzene, toluene, etc. Condensed polycyclic hydrocarbons such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphthacene, picene, perylene, pentaphene and pentacene; derivatives of the above hydrocarbons such as carboxylic acid, carboxylic acid anhydride or carboxylic acid imide; Heteropolycyclic compounds having 3 or more membered rings such as indole, isoindole and quinoline; derivatives of the above-mentioned heteropolycyclic compounds such as carboxylic acid, carboxylic acid anhydride or carboxylic acid imide; and the like. Further, these may partially have a substituent such as a halogen atom, a hydroxyl group, a sulfone group, a nitro group, an amino group and a carboxyl group.

(III) A condensed polycyclic hydrocarbon, a heteropolycyclic compound or the like is heated and pyrolyzed while contacting the carbonaceous material A in a liquid phase to form a carbonaceous material B on the surface layer. Pitch is preferably used as the condensed polycyclic hydrocarbon. Pitch is described in more detail.Ethylene heavy-end pitch generated during naphtha cracking, crude oil pitch generated during crude oil cracking, coal pitch generated during thermal cracking of coal, and asphalt generated by cracking asphalt. Examples include decomposed pitch and pitch produced by thermally decomposing polyvinyl chloride and the like. Further, these various pitches are further heated under an inert gas flow or the like, and the quinoline insoluble content is preferably 80% or more, more preferably 90%.
% Or more, and more preferably 95% or more can be used as a mesophase pitch. In particular, as a method of heating the condensed polycyclic hydrocarbon on the surface of the carbonaceous material A, a method of promoting carbonization through a liquid crystal state called mesophase to form the carbonaceous material B is preferable. The thermal decomposition temperature for forming the carbonaceous material B is 300 to
3,000 ° C. is preferable.

As a method for forming the carbonaceous material B as the surface layer of the carbonaceous material A, a multi-phase surface layer is formed by a multi-step method such as first forming an inner surface layer and then forming an outer surface layer thereon. It is also possible to form a carbonaceous material B of

The proportion of the carbonaceous material A in the thus obtained negative electrode active material for a battery of the present invention is 20 to 95.
Wt% is preferred, more preferably 25-90 wt%,
More preferably 30 to 85% by weight, particularly preferably 3
5 to 80% by weight, most preferably 40 to 75% by weight. The proportion of the carbonaceous material B in the negative electrode active material for a battery of the present invention is preferably 5 to 80% by weight, more preferably 10 to 75% by weight, still more preferably 15 to 70% by weight.
%, Particularly preferably 20 to 65% by weight, most preferably 25 to 60% by weight.

The thickness of the carbonaceous material B, which is the surface layer portion, is preferably 10 nm to 5 μm, more preferably 20 nm.
nm to 4 μm, more preferably 30 nm to 3 μm, particularly preferably 50 nm to 2 μm, most preferably 70 n.
It is m-1.5 micrometers.

Non-Aqueous Electrolyte Battery According to the Present Invention A non-aqueous electrolyte battery comprises a positive electrode containing a positive electrode active material as a main constituent, a negative electrode containing a negative electrode active material for a battery of the present invention as a main constituent, and an electrolyte salt It is composed of a non-aqueous electrolyte contained in a water solvent, and generally a separator is provided between the positive electrode and the negative electrode.

As the non-aqueous electrolyte, those generally proposed for use in lithium batteries and the like can be used. Non-aqueous solvents include cyclic carbonic acid esters such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate;
Cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or its derivatives; 1,3
Ethers such as dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or its derivatives; sulfolane, sultone or One or more derivatives thereof may be mixed, but the mixture is not limited thereto.
Further, the non-aqueous electrolyte preferably contains a carbonate having a double bond. Examples of the carbonate having a double bond include vinylene carbonate, styrene carbonate, catechol carbonate, vinylethylene carbonate, 1-phenylvinylene carbonate, 1,
It is preferable to use 2-diphenylvinylene carbonate or the like alone or in combination of two or more kinds. Particularly, vinylene carbonate is desirable because its effect is remarkable.

As the electrolyte salt, for example, LiCl
O ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSC
N, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ C
l ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr,
Inorganic ion salt containing one kind of lithium (Li), sodium (Na) or potassium (K) such as KClO ₄ and KSCN, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and Li
N (C ₂ F ₅ SO ₂ ) ₂ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄
NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI,
(C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n
_{-C 4 H 9) 4 NI,} (C 2 H 5) 4 N-maleate,
_{(C 2 H 5) 4 N} -benzoate, (C 2 H 5) 4 N-p
Examples thereof include quaternary ammonium salts such as httalate, organic ionic salts such as lithium stearyl sulfonate, lithium octyl sulfonate, lithium dodecylbenzene sulfonate, and the like. These ionic compounds may be used alone or in combination with 2
It is possible to mix and use more than one kind.

As a positive electrode active material which is a main constituent of the positive electrode
Include lithium-containing transition metal oxides and lithium-containing phosphorus.
Acid salt, lithium-containing sulfate, etc., alone or in combination
Is preferred. Lithium-containing transition metal oxide
The general formula Li_yCo_1-xM _xO₂, Li_yNi_1-xM
_xO₂, Li_yMn_2-xM_XO_Four(M is from I to VIII
Metal (for example, Li, Ca, Cr, Ni, Fe, Co
X value indicating the amount of substitution of different elements)
Is effective up to the maximum amount that can be replaced, but is preferable
Or, in terms of discharge capacity, 0 ≦ x ≦ 1. Also, Richiu
For the y value, which indicates the amount of lithium, use lithium reversibly
The maximum amount is effective, preferably 0 from the viewpoint of discharge capacity.
≦ y ≦ 2. ), But is not limited to these
Not something.

Other positive electrode active materials may be mixed with the lithium-containing compound, and other positive electrode active materials include Group I compounds such as CuO, Cu ₂ O, Ag ₂ O, CuS, and CuSO _4. IV of metal compounds, TiS ₂ , SiO ₂ , SnO, etc.
Group metal compound, V ₂ O ₅ , V ₆ O ₁₂ , VO _x , Nb ₂ O ₅ , B
Group V metal compounds such as i ₂ O ₃ and Sb ₂ O ₃ , CrO ₃ and Cr ₂
Group VI metal compounds such as O ₃ , MoO ₃ , MoS ₂ , WO ₃ , and SeO ₂ , Group VII metal compounds such as MnO ₂ , Mn ₂ O ₃ , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , and Ni ₂ O ₃ , NiO,
Group VIII metal compounds such as CoO ₃ and CoO, or
General formula Li _x MX ₂ , Li _x MN _y X ₂ (M and N are from I to V
Group III metal, X represents a chalcogen compound such as oxygen or sulfur. ) Or the like, for example, a metal compound such as a lithium-cobalt-based composite oxide or a lithium-manganese-based composite oxide, and a conductive high material such as disulfide, polypyrrole, polyaniline, polyparaphenylene, polyacetylene, or polyacene-based material. Examples thereof include molecular compounds and quasi-graphite structure carbonaceous materials, but are not limited thereto.

For the negative electrode, it is possible to use other carbonaceous materials in addition to the negative electrode active material for a battery of the present invention. Among them, graphite is preferable because it has an operating potential extremely close to that of metallic lithium, and thus self-discharge can be reduced and irreversible capacity during charge and discharge can be reduced when a lithium salt is used as an electrolyte salt.

In addition to the negative electrode active material for batteries of the present invention and other carbonaceous materials, metal oxides such as tin oxide and silicon oxide, phosphorus, boron and amorphous carbon are added to the negative electrode. It is also possible to do quality. In particular, by modifying the surface of the carbonaceous material by the above method, decomposition of the electrolytic solution can be suppressed and battery characteristics can be improved, which is preferable. Furthermore, in addition to the above-mentioned negative electrode active material for batteries and other carbonaceous materials, lithium metal such as lithium metal, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloy. It is also possible to insert lithium in combination with a contained alloy or the like, or to electrochemically reduce lithium into the negative electrode active material for a battery or another carbonaceous material of the present invention in advance.

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 or ion conductivity, or a compound having a hydrophobic group. For example, gold, silver, carbon, nickel, copper and other substances with good electron conductivity, lithium carbonate,
A material having good ion conductivity such as boron glass and a solid electrolyte, or a material having a hydrophobic group such as silicone oil may be applied by applying techniques such as plating, sintering, mechanofusion, vapor deposition, and 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 preferably 10 μm or less for the purpose of improving the high output characteristics of the non-aqueous electrolyte battery. A crusher or a classifier can be used to obtain the powder in a predetermined shape. Mortar, ball mill,
A sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve or the like is used. Wet grinding in which water and an organic solvent such as hexane are allowed to coexist may be used during grinding. The classification method is not particularly limited, and a sieve, an air classifier, or the like may be used in both dry and wet methods as needed.

The positive electrode active material and the negative electrode material, which are the main constituents of the positive electrode and the negative electrode, have been described above in detail. The positive electrode and the negative electrode contain a conductive agent, a binder and a filler in addition to the main constituents. , May be contained as another component.

The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance, but usually,
Natural graphite (scaly graphite, flake graphite, earth graphite, etc.), artificial graphite, carbon black, acetylene black, Ketjen black, carbon whiskers, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, A conductive material such as a metal fiber or a conductive ceramic material may be contained as one kind or a mixture thereof.

Of these, acetylene black is preferable as the conductive agent from the viewpoint of electron conductivity and coatability. The amount of the conductive agent added is preferably 1% by weight to 50% by weight, particularly 2% by weight to 3% by weight, based on the total weight of the positive electrode or the negative electrode.
0% by weight is preferred. These mixing methods are physical mixing, and ideally, they are homogeneous mixing. Therefore, powder type mixers such as V type mixer, S type mixer, grinding machine, ball mill and planetary ball mill are dry type,
Alternatively, it is possible to mix them by a wet method.

The binder is usually a thermoplastic resin such as polytetrafluoroethylene, polyvinylidene fluoride, polyethylene or polypropylene, ethylene-propylene diene terpolymer (EPDM), sulfonated EPD.
Polymers having rubber elasticity such as M, styrene-butadiene rubber (SBR) and fluororubber, polysaccharides such as carboxymethyl cellulose and the like can be used as one kind or as a mixture of two or more kinds. Further, the binder having a functional group that reacts with lithium like a polysaccharide is preferably deactivated by, for example, methylating. The amount of the binder added is 1 to 5 with respect to the total weight of the positive electrode or the negative electrode.
0 wt% is preferable, and 2 to 30 wt% is particularly preferable.

As the filler, any material may be used as long as it does not adversely affect the battery performance. Usually, olefin polymers such as polypropylene and polyethylene, aerosil, zeolite, glass, carbon and the like are used. The amount of the filler added is preferably 30% by weight or less with respect to 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 or toluene or water, and the resulting mixed solution is described in detail below. It is suitably prepared by coating on and drying. With respect to the coating method, for example, it is preferable to use roller coating such as an applicator roll, screen coating, doctor blade method, spin coating, bar coater, comma coater, die coater, or the like to have any thickness and any shape. However, the present invention is not limited to these.

The current collector may be any electron conductor that does not adversely affect the constructed battery. For example, as the current collector for the positive electrode, aluminum, titanium,
In addition to stainless steel, nickel, baked carbon, conductive polymers, conductive glass, etc., the surface of aluminum, copper, etc. is carbon, nickel, titanium, silver, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance. The product treated with can be used. As the negative electrode current collector, in addition to copper, nickel, iron, stainless steel, titanium, aluminum, baked carbon, conductive polymer, conductive glass, Al-Cd alloy, adhesiveness,
For the purpose of improving conductivity and resistance to reduction, a material obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver or the like can be used. It is also possible to oxidize the surface of these materials.

With respect to the shape of the current collector, in addition to the foil shape, a film shape, a sheet shape, a net shape, a punched or expanded material, a lath material, a porous material, a foamed material, a fiber group forming material, or the like is used. To be There is no particular limitation on the thickness, but 1
Those having a thickness of up to 500 μm are used. Among these current collectors, the positive electrode is an aluminum foil having excellent oxidation resistance, and the negative electrode is a stable copper foil in a reducing field and has excellent electrical conductivity, and an inexpensive copper foil, nickel foil, or iron. Preference is given to using foils and alloy foils containing parts thereof. Further, it is preferable that the foil has a rough surface with a surface roughness of 0.2 μmRa or more, and thereby 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 the electrolytic foil because it has such a rough surface. In particular, an electrolytic foil that has been treated with a hook is most preferable. Further, when both surfaces of the current collector are used, it is preferable that the surface roughness thereof is equal or almost equal.

As the separator, it is preferable to use a porous film or a non-woven fabric having excellent rate characteristics, either alone or in combination. Examples of the material forming the separator include polyolefin resins represented by polyethylene, polypropylene, etc., polyester resins represented by polyethylene terephthalate, polybutylene terephthalate, etc., polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer. , Vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-
Tetrafluoroethylene copolymer, vinylidene fluoride-
Trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride- Examples thereof include trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-ethylene-tetrafluoroethylene copolymer and the like.

The porosity of the separator is 98 from the viewpoint of strength.
Volume% or less is preferable. From the viewpoint of charge / discharge characteristics, the porosity is preferably 20% by volume or more.

As the separator, for example, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methylmethacrylate, vinyl acetate, vinylpyrrolidone, polyvinylidene fluoride and an electrolyte may be used.

Further, it is preferable that the separator is used in combination with the above-mentioned porous membrane, non-woven fabric or the like in combination with the polymer gel, since the liquid retaining property of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the wall surface of the micropores are coated with a hydrophilic solvent polymer having a thickness of several μm or less, and holding an electrolyte in the micropores of the film, the hydrophilic solvent polymer is formed. Gels.

Examples of the solvent-philic polymer include polyvinylidene fluoride, acrylate monomers having an ethylene oxide group or ester group, epoxy monomers, polymers obtained by crosslinking monomers having an isocyanate group, and the like. For the cross-linking, an actinic ray such as an ultraviolet ray (UV) or an electron beam (EB) can be used.

For the purpose of controlling the strength and physical properties, the above-mentioned hydrophilic solvent polymer may be used by blending with a physical property adjusting agent within a range that does not interfere with the formation of a crosslinked product. Examples of the physical property adjusting agent include inorganic fillers {metal oxides such as silicon oxide, titanium oxide, aluminum oxide, magnesium oxide, zirconium oxide, zinc oxide and iron oxide, metal carbonates such as calcium carbonate and magnesium carbonate}. , Polymers {polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc.} and the like. The addition amount of the physical property adjusting agent is usually 50% by weight or less, preferably 20% by weight or less with respect to the crosslinkable monomer.

The non-aqueous electrolyte battery according to the present invention is preferably prepared by injecting the electrolyte, for example, before or after stacking the separator, the positive electrode and the negative electrode, and finally sealing with an exterior material. It is made. Further, in a non-aqueous electrolyte battery in which a power generation element in which a positive electrode and a negative electrode are laminated via a separator is wound, the electrolyte is preferably injected into the power generation element before and after the winding. As the injection method, it is possible to inject at normal pressure, but a vacuum impregnation method or a pressure impregnation method can also be used.

From the viewpoint of reducing the weight of the non-aqueous electrolyte battery, the exterior material is preferably a thin material, for example, a metal-resin composite film in which a metal foil is sandwiched between resin films. Specific examples of the metal foil include aluminum,
Iron, nickel, copper, stainless steel, titanium, gold, silver, etc.
The foil is not limited as long as it is a pinhole-free foil, but a lightweight and inexpensive aluminum foil is preferable. As the resin film on the outside of the battery, a resin film having excellent puncture strength such as polyethylene terephthalate film or nylon film can be heat-sealed as the resin film on the inside of the battery such as polyethylene film or nylon film. A film that is present and has solvent resistance is preferable.

[0057]

The details of the present invention will be described below with reference to examples, but the present invention is not limited thereto.

Here, a method of calculating the rhombohedral crystal structure contained in the entire graphite crystal, which is described in Japanese Patent Laid-Open No. 2000-348727, will be described. The peak area of the (101) diffraction line attributed to the rhombohedral crystal structure measured by the X-ray wide-angle diffraction method is r ₍₁₀₁₎ , and the (101) diffraction line attributed to the hexagonal structure measured in the same manner. The peak area of ₍₁₎ is defined as h _(101), and the content ratio R% of the rhombohedral crystal structure in the entire graphite crystal is calculated by the following equation.

[0059]

[Formula 1] (Example 1) Artificial graphite having an Lc of 100 nm or more was pulverized by the Gakushin method so that the average particle size was 20 μm. The specific surface area of this crushed artificial graphite was 5 m ² / g. The content ratio of the rhombohedral crystal structure in the crushed artificial graphite was calculated by the above method, and was 15%. A layer made of the carbonaceous material B is formed on the surface of the crushed artificial graphite by mixing the artificial graphite and polyvinyl alcohol in a weight ratio of 1: 1 and firing the mixture at 1000 ° C. for 5 hours in a high-purity argon atmosphere. Let Thus, the negative electrode active material for a battery of the present invention was produced. The specific surface area of the negative electrode active material for a battery was 2.5 m ² / g. The thickness of the carbonaceous material B was about 1 μm.

Example 2 A non-aqueous electrolyte battery was produced according to the following procedure.

The positive electrode was manufactured as follows. LiCoO ₂ as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder,
After mixing in a weight ratio of 94: 3: 3, a positive electrode slurry was prepared using N-methylpyrrolidone as a solvent. The positive electrode slurry was applied to both sides of a 20 μm aluminum foil as a positive electrode current collector, and N-methylpyrrolidone was removed by drying, followed by pressing with a roll press,
A positive electrode was obtained.

The negative electrode was manufactured as follows. The negative electrode active material for a battery of the present invention prepared in Example 1, carboxymethyl cellulose as a binder and styrene-butadiene rubber as a binder were kneaded with purified water to a weight ratio of 98: 1: 1. A negative electrode slurry of the above material was prepared. The negative electrode slurry was applied as a negative electrode current collector to both sides of an electrolytic copper foil having a surface roughness of 0.3 μmRa and dried. This negative electrode plate was pressed by a roll press to obtain a negative electrode.

The separator was manufactured as follows.
First, an ethanol solution in which 3% by weight of a bifunctional acrylate monomer having the structure shown in (Chemical Formula 1) was dissolved was prepared, and a polyethylene microporous membrane (average pore diameter 0.1 μm, porosity 50%) as a porous substrate , Thickness 23μm, weight 1
After coating with 2.52 g / m ² and air permeability of 89 seconds / 100 ml), the monomer was crosslinked by electron beam irradiation to form an organic polymer layer, and dried at a temperature of 60 ° C. for 5 minutes. A separator was obtained through the above steps. The obtained separator had a thickness of 24 μm and a weight of 13.04 g /
m ² , air permeability of 103 seconds / 100 ml, the weight of the organic polymer layer is about 4% by weight with respect to the weight of the porous material,
The thickness of the crosslinked body layer was about 1 μm, and the pores of the porous substrate were maintained almost as they were.

[0064]

[Chemical 1] Aluminum plate as positive electrode terminal (width 5 mm, thickness 10
0 μm) and a nickel plate as a negative electrode terminal (width 5 mm,
A thickness of 100 μm) was connected to the positive electrode current collector and the negative electrode current collector, respectively, by electric resistance welding, and the positive electrode and the negative electrode were wound via the separator to obtain a power generating element.

As the outer package, a tubular metal-resin composite film laminated with a polyethylene terephthalate outer resin, an aluminum foil and a modified polypropylene inner resin was used, and the power generating element was placed therein.

The non-aqueous electrolyte is propylene carbonate,
LiP was added to a mixed solvent in which ethylene carbonate and vinylene carbonate were mixed at a volume ratio of 49: 49: 2.
Obtained by dissolving F ₆ at a concentration of 2 mol / l.

The non-aqueous electrolyte of the present invention was produced by injecting the non-aqueous electrolyte into the exterior body in which the power-generating element was placed under a reduced pressure of 1333 Pa, and further sealing under a reduced pressure of 1333 Pa. did. Design capacity is 500m
It is Ah. This is designated as Battery A of the present invention. (Example 3) Except that a non-aqueous electrolyte prepared by dissolving LiPF ₆ at a concentration of 1 mol / liter in a mixed solvent in which diethyl carbonate and ethylene carbonate were mixed at a volume ratio of 50:50 was used. A non-aqueous electrolyte battery was produced in the same manner as in Example 2. This is designated as Battery B of the invention.

(Comparative Example 1) The same as Example 2 except that the negative electrode active material for a battery of the present invention was replaced with ground artificial graphite that was not coated with the carbonaceous material B. An attempt was made to produce a non-aqueous electrolyte battery by the procedure, but in the step of producing the negative electrode, the negative electrode slurry produced by applying the negative electrode slurry prepared in the same manner as in Example 2 with the binder ratio to the negative electrode current collector was dried, However, the negative electrode active material was easily peeled off from the current collector, and the battery could not be assembled using this.

(Comparative Example 2) In the step of producing a negative electrode, crushed artificial graphite not coated with the carbonaceous material B, carboxymethyl cellulose as a binder, and styrene-butadiene rubber as a binder were used.
A non-aqueous electrolyte battery was produced in the same manner as in Example 2 except that a negative electrode slurry of the above material was produced by kneading with purified water so that the weight ratio was 1.5: 2. . This is designated as Comparative Battery C.

(Comparative Example 3) Average particle size 20 μm; Rhombohedral structure content 0%; Crystallite size (Lc) in c-axis direction 70 nm; Specific surface area 3.5 m ² / g The artificial graphite and polyvinyl alcohol are mixed in a weight ratio of 1: 1 and baked at 1000 ° C. for 5 hours in a high-purity argon atmosphere to form a layer made of the carbonaceous material B on the surface of the artificial graphite. Then, a negative electrode active material of Comparative Example 3 was obtained. The specific surface area was 3 m ² / g.

A non-aqueous electrolyte battery was produced in the same procedure as in Example 2 except that the negative electrode active material of Comparative Example 3 was used in place of the battery negative electrode active material of the present invention. This is designated as Comparative Battery D.

(Battery Performance Test) The discharge capacities at 20 ° C. and −20 ° C. were measured using the batteries A and B of the present invention and the comparative batteries C and D. Charging was 4.2V at 20 ° C., 5 hour rate (0.2 ItmA), constant current constant voltage charging for 7 hours, and discharging was at a final voltage of 2.7 V and 1 at 20 ° C. and −20 ° C., respectively. 0.0 hour rate (1
ItmA) constant current discharge. The "energy density" was calculated based on the capacity obtained by discharging at 20 ° C.

-20 ° C to discharge capacity at 20 ° C
The ratio of the discharge capacity in the above was determined as a "low temperature performance value" in percentage. The results are shown in Table 1.

The rate characteristics at 20 ° C. were measured. Charging is 4.2V at 20 ° C, 1 hour rate (1 Itm
A), constant-current constant-voltage charging for 2 hours, discharging was performed at a final voltage of 2.7 V at 20 ° C. and a 2-hour rate (0.5 It).
mA), 1 hour rate (1 ItmA), 0.5 hour rate (2I)
tmA) and 0.33 hour rate (3 ItmA) of each current. The ratio of the discharge capacity at each discharge current to the discharge capacity at a discharge current 5 hour rate (0.2 ItmA) was evaluated as a percentage.

The cycle characteristics at 20 ° C. were measured.
Charging is 4.2V at 20 ° C, 1 hour rate (1 Itm
A), constant-current constant-voltage charging for 2 hours, discharging at 20 ° C. with a final voltage of 2.7 V, 1-hour rate (1 ItmA), and the number of cycles reduced to 70% of the initial capacity is called “cycle life”. did.

The above results are shown in Table 1. The test of the comparative battery D was stopped because the battery swelled during the first cycle of charging.

[0077]

[Table 1] As shown in Table 1, it is understood that the battery A of the present invention has a higher energy density and excellent cycle characteristics and rate characteristics as compared with the comparative battery C. That is, by using graphite having a rhombohedral structure of 15% or more in the negative electrode, decomposition of propylene carbonate is suppressed, and by covering with a carbonaceous material, charging / discharging efficiency is improved, so that the energy density is high, The battery has excellent cycle characteristics. Further, since the specific surface area of the negative electrode material is 3 m ² / g or less, it is possible to reduce the amount of the binder in the negative electrode, and as a result, it is possible to improve the rate characteristic.

On the other hand, in Comparative Battery D using graphite containing no rhombohedral system structure, decomposition of propylene carbonate could not be suppressed during the first charging, and decomposition gas was generated during charging. Conceivable.

Further, comparing the batteries A and B of the present invention,
It can be seen that by including propylene carbonate in addition to vinylene carbonate, which is a carbonate containing a double bond, in the non-aqueous electrolyte, the solidification of the electrolyte was suppressed even at -20 ° C, and the low temperature performance was improved.

That is, it was confirmed that the battery of the present invention has a high energy density and is excellent in cycle characteristics, rate characteristics and low temperature performance.

[0081]

As described above, according to the present invention, the rhombohedral crystal is formed on the surface of the carbonaceous material A made of graphite containing 15% or more of the rhombohedral crystal structure according to the present invention. By using the negative electrode active material for a battery, which is coated with the carbonaceous material B containing no system structure, a non-aqueous electrolyte battery having both high energy density and excellent cycle characteristics can be provided.

According to the present invention, as described in claim 2, the carbonaceous material A has Lc showing the size of a crystallite of 100 nm or more, and the negative electrode active material for a battery is BET. When the value of the specific surface area by the method is 3 m ² / g or less, it is possible to provide a non-aqueous electrolyte battery having improved rate characteristics.

Further, according to the present invention, as described in claims 3 and 4, the low-temperature performance is improved by the non-aqueous electrolyte containing a carbonate having at least a double bond and further containing propylene carbonate. A non-aqueous electrolyte battery can be provided.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroe Nakagawa             2-32 Kosobe-cho, Takatsuki City, Osaka Prefecture Stock             Ceremony company Yuasa Corporation F-term (reference) 4G046 EA05 EC00 EC05                 5H029 AJ02 AJ03 AJ05 AK02 AK03                       AK05 AK06 AK16 AK18 AL06                       AL07 AL18 AM02 AM03 AM04                       AM05 AM07 CJ22 DJ16 DJ17                       HJ01 HJ07 HJ13                 5H050 AA02 AA06 AA07 AA08 BA17                       CA02 CA03 CA04 CA05 CA08                       CA09 CA11 CA14 CA20 CA21                       CA22 CA29 CB07 CB08 CB29                       DA03 EA08 FA17 FA18 FA19                       GA22 HA01 HA07 HA13

Claims (4)

[Claims] 1. A negative electrode active material for a battery, wherein the surface of a carbonaceous material A made of graphite containing 15% or more of a rhombohedral structure is coated with a carbonaceous material B not containing a rhombohedral structure. 2. The carbonaceous material A has an Lc indicating a crystallite size of 100 nm or more, and the negative electrode active material for a battery has a specific surface area value by BET method of 3 m ² / g or less. Item 11. A negative electrode active material for a battery according to item 1. 3. A negative electrode produced by using the negative electrode active material for a battery according to claim 1, a positive electrode, and a non-aqueous electrolyte containing a carbonate having a double bond. And a non-aqueous electrolyte battery. 4. The non-aqueous electrolyte battery according to claim 3, wherein the non-aqueous electrolyte contains at least propylene carbonate.