CA2184678C - Non-aqueous electrolyte secondary battery - Google Patents
Non-aqueous electrolyte secondary battery Download PDFInfo
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- CA2184678C CA2184678C CA002184678A CA2184678A CA2184678C CA 2184678 C CA2184678 C CA 2184678C CA 002184678 A CA002184678 A CA 002184678A CA 2184678 A CA2184678 A CA 2184678A CA 2184678 C CA2184678 C CA 2184678C
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/24—Alkaline accumulators
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/626—Metals
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/70—Carriers or collectors characterised by shape or form
- H01M4/80—Porous plates, e.g. sintered carriers
- H01M4/806—Nonwoven fibrous fabric containing only fibres
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/668—Composites of electroconductive material and synthetic resins
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M6/00—Primary cells; Manufacture thereof
- H01M6/14—Cells with non-aqueous electrolyte
- H01M6/16—Cells with non-aqueous electrolyte with organic electrolyte
- H01M6/162—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte
- H01M6/164—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte by the solvent
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Manufacturing & Machinery (AREA)
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- Battery Electrode And Active Subsutance (AREA)
Abstract
The present invention relates to a non-aqueous electrolyte secondary battery. The graphitized vapor-grown carbon fibers used as an anode in the present invention have a specific surface area of at most 5 m2/g and an average aspect ratio of 2-30. The non-aqueous electrolyte secondary battery comprises an anode comprising a cathode comprising a lithium-containing complex oxide, an anode comprising the graphitized vapor-grown carbon fibers, and an electrolyte comprising a lithium salt and a solvent. The present invention provides a non-aqueous electrolyte secondary battery having a high capacity maintained over a broad temperature range, good cycle characteristics, a high safety and an improved load characteristics.
Description
NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a non-aqueous electro-lyte secondary battery, more particularly to a non-aqueous electrolyte secondary battery with improved safety and load characteristics.
Description of Related Art Vapor-grown carbon fibers may be produced by thermally decomposing carbon compounds at a temperature of 800-1300 C
in the presence of ultrafine iron and nickel as catalyst.
These vapor-grown carbon fibers are characterized by being easily converted into graphite by heat treatment. For example, graphitized vapor-grown carbon fibers obtained by heat treatment at a temperature exceeding 2800 C have a less amount of crystal defects, a network of carbon hexagonal lattices growing tubularly around the axis of a fiber, further similar networks layered on the network outwardly and concentrically, like growth rings of a tree. Therefore, these graphitized vapor-grown carbon fibers are highly strong and elastic, and thermally and electrically conduc-tive.
One of applications of these graphitized vapor-grown carbon fibers may be a non-aqueous electrolyte secondary battery, in which these carbon fibers are used as an elec-trode active material.
The non-aqueous electrolyte secondary battery is nor-mally comprised of an anode, separator, cathode and electro-lyte. As materials used for the anode reference may be made to natural graphite, artificial graphite, hardly-graphitiza-ble carbon which is the so-called hard carbon, mesocarbon microbeads, pitch carbon fibers and vapor-grown carbon fibers. As materials used for the cathode reference may be made to a lithium-containing complex oxide such as lithium cobaltate (LiCo02), lithium manganate (LiMn2O4, LiMnO2) and lithium nickelate (LiNiO2). For the electrolyte may be used a non-aqueous electrolyte comprising a mixture of a lithium salt and an organic solvent. As the lithium salt reference may be made to LiC104, LiPF6, LiBF4, LiAsF6 and LiCF3SO3.
As the organic solvent reference may be made to ethylene carbonate (hereinbelow often referred to as EC), propylene carbonate (hereinbelow often referred to as PC), dimethyl carbonate (hereinbelow often referred to as DMC), diethyl carbonate (hereinbelow often referred to as DEC) and methy-lethyl carbonate (hereinbelow often referred to as MEC).
Recently, the non-aqueous electrolyte secondary batter-ies having excellent cycle properties have attracted atten-tion as large-sized batteries for electric vehicles and domestic electricity storage systems.
In a lithium ion secondary battery, lithium is general-ly precipitated at the surface of the anode thereof in the form of needles and they sometimes pierce a separator placed between the cathode and the anode when the battery is over-charged, charging current is too heavy, or the like, so that short-circuits can easily be formed. As a result, the lithium ion secondary battery may burst or ignite. Further-more, overcharging may cause the electrolyte to be decom-posed, so that the cycle life of the lithium ion secondary battery may be reduced. On the other hand, overdischarging the battery makes a conductor having an electrode coated with active materials dissolved, so that the cycle life of the lithium ion secondary battery is highly reduced. In order to avoid these problems, lithium ion secondary batter-ies are equipped with a safety device for preventing the overcharging and overdischarging.
An organic solvent including a linear carbonate which has a low viscosity, e.g. a mixture of a cyclic carbonate such as ethylene carbonate and propylene carbonate with a linear carbonate, has conventionally been employed as the organic solvent for the purpose of improving a lithium ion _ .. .._,..
2 f~46T8 secondary battery's properties at a low temperature and cycle characteristics. Prior art lithium ion secondary batteries using such a solvent as the above-mentioned have a problem in safety. The problem in safety is that the charged batteries are broken by gases formed by decomposi-tion of the solvent in the batteries and then ignited, because of a high temperature of the lithium ion secondary battery caused by a heavy current when, for example, the above-mentioned short-circuits are formed, artificial short-circuits are formed in a nailing test, or the like.
One of the causes is that the linear carbonate has a low boiling point and a high vapor pressure, and another that an exposed area or active reaction area of a fracture of graph-ite crystal in the anode promotes the decomposition of the solvent, particularly an electrolytic decomposition of propylene carbonate which leads to production of gases, in other words, acts a catalyst in the decomposition, and further that if the anode has an insufficient designed capacity, then lithium will be precipitated at the anode.
Prior art lithium ion secondary batteries have unsatis-factory electric conductivity as well as poor cycle charac-teristics. Therefore, one has demanded secondary batteries having good cycle characteristics as well as high stability at a high load, i.e., having a high capacity in charging and discharging at a major current.
In order to improve conductivity of the electrodes, particularly the anode, a small amount of materials for improving conductivity has been added to the electrodes.
The addition, however, lowers a relative amount of active materials in an electrode, which leads to a decrease in a capacity of the battery. Further, the present inventors found that the addition itself raised unsafeness of the bat-tery. The reason is considered as follows. Materials for improving conductivity have a very great specific surface ratio, which differs widely from that of vapor-grown carbon fibers. Therefore addition of a very small amount of the materials to an electrode will increase an average specific surface ratio of the active materials in the electrode.
SUMMARY OF THE INVENTION
The primary object of the present invention is to solve a problem which will be caused when a linear carbonate such as dimethyl carbonate (hereinbelow often abbreviated as DMC) and diethyl carbonate (hereinbelow often abbreviated as DEC) is employed as one constituent of the mixed solvent and to provide a non-aqueous electrolyte secondary battery having an excellent safety and load characteristics.
The second object of the present invention is to provide a long-life non-aqueous electrolyte secondary battery.
The third object of the present invention is to provide a non-aqueous electrolyte secondary battery allowed to have a high safety by preventing the decomposition of the solvent.
The fourth object of the present invention is to provide a non-aqueous electrolyte secondary battery free of bursting and ignition.
The fifth object of the present invention is to provide a non-aqueous electrolyte secondary battery using a highly electrically conductive electrode and having good cycle characteristics and a high stability under a higher load, i.e., a high capacity even in charging and discharging at a major current.
The present inventors found that load characteristics of a non-aqueous electrolyte secondary battery are improved by selecting vapor-grown carbon fibers as graphite, further selecting vapor-grown carbon fibers having special properties out of the selected ones, setting a packing density of the vapor-grown carbon fibers in an electrode to within a special range, selecting substances for the electrolyte. They further found that safety of a non-aqueous electrolyte secondary battery is influenced by properties of vapor-grown carbon fibers, a packing density of the vapor-grown carbon fibers in an electrode, a ratio of a capacity of the cathode and that of the anode.
An aspect of the present invention is a non-aqueous electrolyte secondary battery comprising an anode made of a compacted body of graphitized vapor-grown carbon fibers having a specific surface area of at most 5 m2/g and an average aspect ratio of 2-30, having a packing density of 1.2-2.0 g/cm3, a cathode made of a lithium-containing complex oxide and an electrolyte comprising a mixed solvent of a cyclic carbonate and a linear carbonate containing a lithium salt therein.
Another aspect of the present invention is a non-aqueous electrolyte secondary battery comprising an anode made of graphitized vapor-grown carbon fibers having a specific surface area of at most 5 m 2/g and an average aspect ratio of 2-30, a cathode made of a lithium-containing complex oxide and an electrolyte comprising a mixed solvent of a cyclic carbonate and a linear carbonate containing a lithium salt therein, wherein a designed capacity of the anode is greater than that of the cathode.
According to a further broad aspect of the present invention there is provided a non-aqueous electrolyte secondary battery. The battery comprises ari anode comprising an electrode comprising an electric conductor with a first thickness value and a pressed compact of graphitized vapor-grown carbon fibers bonded to each other by a binder, wherein said carbon fibers have a specific surface area of at most 5 m2/g and an average aspect ratio of 2-30, and said compact has a packing density of 1.2-2.0 g/cm3 measured by a method comprising cutting said electrode into a piece with a predetermined width and a predetermined length, measuring a second thickness value of said piece and the weight thereof, and calculating said packing density from said width, length, said first and second thickness values, and the weight; a cathode comprising a lithium-- 5a -containing complex oxide; and an electrolyte comprising a mixed solvent of a cyclic carbonate and a linear carbonate including a lithium salt dissolved therein.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph showing a relation between current and discharge capacity in the charging-discharging cycle tests in accordance with Examples 1, 2, 3 and 6.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
(1) Anode The anode used in the non-aqueous electrolyte secondary battery may have a compacted body comprising pressed graphitized vapor-grown carbon fibers.
Furthermore, the anode may preferably be shaped from a compacted body comprisirig an electric conductor coated with active materials, the active materials forming an active material layer on the surface of the conductor. The active materials are comprised of the graphitized vapor-grown 1i846/8 carbon fibers bonded each other by a binder.
(1-1) Graphitized Vapor-grown Carbon Fibers The graphitized vapor-grown carbon fibers used for an anode in the present invention has a specific surface area of at most 5 m2/g, preferably at most 3 m2/g, more prefera-bly at most 2 m2/g. If the specific surface area exceeds 5 m2/g, the objects of the present invention cannot be achieved, and the charge and discharge efficiency and/or cycle life is reduced to such an extent that the battery cannot be put into practice. In the other words, if the graphitized vapor-grown carbon fibers have a specific sur-face area of not more than 5 m2/g, they are advantageous compared with a plate-like graphite, a spherical graphite such as mesocarbon microbeads and a mesocarbon fiber. The reason is as follows. A graphitized vapor-grown carbon fiber has tubular networks of carbon hexagonal lattices, which networks are layered concentrically with the axis of the fiber, like growth rings of a tree. A graphitized vapor-grown carbon fiber which has been cut so as to have an aspect ratio of 2-30 has exposed parts of fracture of the graphite crystal, or the carbon lattices, only on the both ends, which lowers the fiber's function of catalyzation of the electrolysis of the solvent. On the other hand, when a plate-like graphite is used, all of the sides are the ex-posed parts of fracture of the graphite crystal and when other shapes of graphite are used, almost all of the surface are the exposed parts. Therefore, these graphites deterio-rate in safety.
Further, if the specific surface area of the graphi-tized vapor-phase grown carbon fibers is at most 5 m2/g, acceleration or catalyzation of the decomposition of the solvent with the exposed area of fracture of the graphite crystal, i.e., the fracture active reaction area of the anode can greatly be prevented.
When the specific surface area exceeds 5 m2/g, a large 2184,678 amount of white smoke to such an extent that the cathode cap is broken may be emitted if both the electrodes should make a short circuit.
To the contrary, if the specific surface area is at most 5 m2/g, an amount of smoke can greatly be decreased and the cap can be prevented from being broken.
In addition, a graphitized vapor-grown carbon fiber was used in a specific packing density, conductivity of the anode increases. Thus, addition of materials for improving conductivity, such as acetylene black, which is a high conductive carbon black having a remarkably great specific surface area is not necessary, which leads to a marked increase of safety of the battery.
The specific surface area may be determined by the BET
method.
The average aspect ratio of the graphitized vapor-phase grown carbon fibers is in the range of 2-30, preferably 3-20, more preferably 5-15. If the average aspect ratio is in the specified range, then the objects of the present inven-tion can be achieved well. In other words, the average aspect ratio exceeds 30, then there occurs such inconven-ience that the electrode cannot be formed in a sheet and a packing density of the anode is lowered, which leads to deterioration in load characteristics and safety. If the average aspect ratio is less than 2, then the specific surface area is inconveniently more than 5 m2/g.
If the average aspect ratio is in the range of 2-30, the graphitized vapor-phase grown carbon fibers are brought in contact with each other to such an extent that the elec-trode itself can have a high electric conductivity. This does not cause any great potential difference between the current collector and the surface of the electrode even when a heavy current flows at a high load. That is, uniform charging-discharging between the core and the surface of the electrode is possible, so that the charge capacity and the discharge capacity are increased. Thus, the present inven-Ll0140f0 tion can provide a non-aqueous electrolyte secondary battery exhibiting a high capacity in charging and discharging at a heavy current.
If the average aspect ratio is less than 2, the contact resistance is so large that the electric conductivity is reduced. If the average aspect ratio exceeds 30, then the packing density of the electrode is lowered, so that the electric conductivity of the electrode decreases. When the average aspect ratio is less than 2 or exceeds 30, the electric conductivity of the electrode decreases, which results in decrease in performance of the battery. As mentioned above, in conventional art, the materials for im-proving conductivity had to be added in order to make con-ductivity of the electrode greater. When the average aspect ratio is within the range, electric conductivity of the electrode itself becomes increased. Thus, addition of the materials for improving conductivity can be obviated and a non-aqueous electrolyte secondary battery with improved safety can be provided.
The graphitized vapor-grown carbon fibers are normally have an average diameter of 1-10 m, preferably 2-5 m. The average diameter in the range of 1-10 m allows the disper-sion of the fibers with a binder in an organic solvent to easily be realized and the fibers to be easily brought into contact with each other. This leads to increase in conduc-tivity of the anode with a specific packing density and to unnecessariness of adding a carbon black which is a material for improving conductivity, e.g. acetylene black. Surpris-ingly, conductivity of the anode according to the present invention is greater than that of an anode made of other graphites with addition of the materials for improving conductivity. The anode of the invention has no increase in a specific surface area by adding the materials. Both of the advantages lead to a increased safety of the non-aqueous electrolyte secondary battery.
The average aspect ratio of the graphitized vapor-grown carbon fibers is determined by taking electron microphoto-graphs of one thousand samples of the carbon fibers selected at random, measuring the length and the diameter of the selected carbon fibers, on the supposition that these carbon fibers are in a tubular form, calculating the aspect ratio from the length and the diameter for each sample, and aver-aging the calculated thousand aspect ratios. The average diameter of the carbon fibers is determined by measuring the diameter of the selected carbon fibers, and averaging the measurements of one thousand samples.
The graphitized vapor-grown carbon fibers used in the present invention have a graphite crystal structure de-veloped to a high degree and normally have a graphite net-work distance (d002), which is a distance between adjacent networks, of at most 0.338nm, preferably at most 0.337 nm, more preferably 0.3355-0.3365 nm, in view of the degree of development of a graphite network having a pattern of multi-ple hexagonal ri..ngs.
Furthermore, the graphitized vapor-grown carbon fibers used in the present invention have a thickness of the lay-ered graphite networks, i.e., a thickness of a crystallite (Lc) normally of at least 40 nm, preferably 60 nm, more preferably 80 nm.
The graphitized vapor-grown carbon fibers having a graphite network distance exceeding 0.338 nm, or a thickness of a graphite crystallite of less than 40 nm do not interca-late a sufficient amount of lithium ions and, therefore, are sometimes inconveniently used as an anode for lithium ion secondary batteries.
The graphite network distance and the thickness of the crystallite may be determined by the "Gakushinhou" method, which is proposed by Japan Society for the Promoting of Science, and is described on page 55 of "Tanso Gijutsu (Carbon Technology) I" published by Kagaku Gijutsu Shuppan-sha, 1970.
The graphitized vapor-grown carbon fibers used in the present invention has a spin density preferably in the range of at greatest 8x1018 spins/g, more preferably at greatest 7x1018 spins/g, as determined by the electron spin resonance absorption method.
The graphitized vapor-grown carbon fibers specified by the present invention may preferably be produced by fractur-ing starting graphitized vapor-grown carbon fibers in some form at a high impact strength or pressing the carbon fibers under hydrostatic pressure.
The graphitized vapor-grown carbon fibers can be pro-duced by graphitizing carbon fibers obtained by vapor-growth.
The vapor-grown carbon fibers can be produced by a vapor-growth method.
Specifically, the vapor-grown carbon fibers may be produced by the methods described in JP-A-52-107320, JP-A-57-117622, JP-A-58-156512, JP-A-58-180615, JP-A-60-185818, JP-A-60-224815, JP-A-60-231821, JP-A-61-132630, JP-A-61-132600, JP-A-61-132663, JP-A-61-225319, JP-A-61-225322, JP-A-61-225325, JP-A-61-225327, JP-A-61-225328, JP-A-61-275425, JP-A-61-282427 and JP-A-5-222619.
The graphitized vapor-grown carbon fibers may be pro-duced by heat treating the starting vapor-grown carbon fibers at a temperature in the range of not lower than 2000 C, preferably 2000 C-3000 C.
Fine starting vapor-grown carbon fibers which are not greater than 70 nm in diameter sometimes have graphite crystals or carbon lattices having sufficiently been grown when they are produced by the above-mentioned methods. The fine starting vapor-grown carbon fibers can be used for the anode without the heat treating, as well as the graphitized vapor-grown carbon fibers.
Normally, the atmosphere for the heat treatment may be an inert gas, and the heat treating time may be 5 minutes or more.
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a non-aqueous electro-lyte secondary battery, more particularly to a non-aqueous electrolyte secondary battery with improved safety and load characteristics.
Description of Related Art Vapor-grown carbon fibers may be produced by thermally decomposing carbon compounds at a temperature of 800-1300 C
in the presence of ultrafine iron and nickel as catalyst.
These vapor-grown carbon fibers are characterized by being easily converted into graphite by heat treatment. For example, graphitized vapor-grown carbon fibers obtained by heat treatment at a temperature exceeding 2800 C have a less amount of crystal defects, a network of carbon hexagonal lattices growing tubularly around the axis of a fiber, further similar networks layered on the network outwardly and concentrically, like growth rings of a tree. Therefore, these graphitized vapor-grown carbon fibers are highly strong and elastic, and thermally and electrically conduc-tive.
One of applications of these graphitized vapor-grown carbon fibers may be a non-aqueous electrolyte secondary battery, in which these carbon fibers are used as an elec-trode active material.
The non-aqueous electrolyte secondary battery is nor-mally comprised of an anode, separator, cathode and electro-lyte. As materials used for the anode reference may be made to natural graphite, artificial graphite, hardly-graphitiza-ble carbon which is the so-called hard carbon, mesocarbon microbeads, pitch carbon fibers and vapor-grown carbon fibers. As materials used for the cathode reference may be made to a lithium-containing complex oxide such as lithium cobaltate (LiCo02), lithium manganate (LiMn2O4, LiMnO2) and lithium nickelate (LiNiO2). For the electrolyte may be used a non-aqueous electrolyte comprising a mixture of a lithium salt and an organic solvent. As the lithium salt reference may be made to LiC104, LiPF6, LiBF4, LiAsF6 and LiCF3SO3.
As the organic solvent reference may be made to ethylene carbonate (hereinbelow often referred to as EC), propylene carbonate (hereinbelow often referred to as PC), dimethyl carbonate (hereinbelow often referred to as DMC), diethyl carbonate (hereinbelow often referred to as DEC) and methy-lethyl carbonate (hereinbelow often referred to as MEC).
Recently, the non-aqueous electrolyte secondary batter-ies having excellent cycle properties have attracted atten-tion as large-sized batteries for electric vehicles and domestic electricity storage systems.
In a lithium ion secondary battery, lithium is general-ly precipitated at the surface of the anode thereof in the form of needles and they sometimes pierce a separator placed between the cathode and the anode when the battery is over-charged, charging current is too heavy, or the like, so that short-circuits can easily be formed. As a result, the lithium ion secondary battery may burst or ignite. Further-more, overcharging may cause the electrolyte to be decom-posed, so that the cycle life of the lithium ion secondary battery may be reduced. On the other hand, overdischarging the battery makes a conductor having an electrode coated with active materials dissolved, so that the cycle life of the lithium ion secondary battery is highly reduced. In order to avoid these problems, lithium ion secondary batter-ies are equipped with a safety device for preventing the overcharging and overdischarging.
An organic solvent including a linear carbonate which has a low viscosity, e.g. a mixture of a cyclic carbonate such as ethylene carbonate and propylene carbonate with a linear carbonate, has conventionally been employed as the organic solvent for the purpose of improving a lithium ion _ .. .._,..
2 f~46T8 secondary battery's properties at a low temperature and cycle characteristics. Prior art lithium ion secondary batteries using such a solvent as the above-mentioned have a problem in safety. The problem in safety is that the charged batteries are broken by gases formed by decomposi-tion of the solvent in the batteries and then ignited, because of a high temperature of the lithium ion secondary battery caused by a heavy current when, for example, the above-mentioned short-circuits are formed, artificial short-circuits are formed in a nailing test, or the like.
One of the causes is that the linear carbonate has a low boiling point and a high vapor pressure, and another that an exposed area or active reaction area of a fracture of graph-ite crystal in the anode promotes the decomposition of the solvent, particularly an electrolytic decomposition of propylene carbonate which leads to production of gases, in other words, acts a catalyst in the decomposition, and further that if the anode has an insufficient designed capacity, then lithium will be precipitated at the anode.
Prior art lithium ion secondary batteries have unsatis-factory electric conductivity as well as poor cycle charac-teristics. Therefore, one has demanded secondary batteries having good cycle characteristics as well as high stability at a high load, i.e., having a high capacity in charging and discharging at a major current.
In order to improve conductivity of the electrodes, particularly the anode, a small amount of materials for improving conductivity has been added to the electrodes.
The addition, however, lowers a relative amount of active materials in an electrode, which leads to a decrease in a capacity of the battery. Further, the present inventors found that the addition itself raised unsafeness of the bat-tery. The reason is considered as follows. Materials for improving conductivity have a very great specific surface ratio, which differs widely from that of vapor-grown carbon fibers. Therefore addition of a very small amount of the materials to an electrode will increase an average specific surface ratio of the active materials in the electrode.
SUMMARY OF THE INVENTION
The primary object of the present invention is to solve a problem which will be caused when a linear carbonate such as dimethyl carbonate (hereinbelow often abbreviated as DMC) and diethyl carbonate (hereinbelow often abbreviated as DEC) is employed as one constituent of the mixed solvent and to provide a non-aqueous electrolyte secondary battery having an excellent safety and load characteristics.
The second object of the present invention is to provide a long-life non-aqueous electrolyte secondary battery.
The third object of the present invention is to provide a non-aqueous electrolyte secondary battery allowed to have a high safety by preventing the decomposition of the solvent.
The fourth object of the present invention is to provide a non-aqueous electrolyte secondary battery free of bursting and ignition.
The fifth object of the present invention is to provide a non-aqueous electrolyte secondary battery using a highly electrically conductive electrode and having good cycle characteristics and a high stability under a higher load, i.e., a high capacity even in charging and discharging at a major current.
The present inventors found that load characteristics of a non-aqueous electrolyte secondary battery are improved by selecting vapor-grown carbon fibers as graphite, further selecting vapor-grown carbon fibers having special properties out of the selected ones, setting a packing density of the vapor-grown carbon fibers in an electrode to within a special range, selecting substances for the electrolyte. They further found that safety of a non-aqueous electrolyte secondary battery is influenced by properties of vapor-grown carbon fibers, a packing density of the vapor-grown carbon fibers in an electrode, a ratio of a capacity of the cathode and that of the anode.
An aspect of the present invention is a non-aqueous electrolyte secondary battery comprising an anode made of a compacted body of graphitized vapor-grown carbon fibers having a specific surface area of at most 5 m2/g and an average aspect ratio of 2-30, having a packing density of 1.2-2.0 g/cm3, a cathode made of a lithium-containing complex oxide and an electrolyte comprising a mixed solvent of a cyclic carbonate and a linear carbonate containing a lithium salt therein.
Another aspect of the present invention is a non-aqueous electrolyte secondary battery comprising an anode made of graphitized vapor-grown carbon fibers having a specific surface area of at most 5 m 2/g and an average aspect ratio of 2-30, a cathode made of a lithium-containing complex oxide and an electrolyte comprising a mixed solvent of a cyclic carbonate and a linear carbonate containing a lithium salt therein, wherein a designed capacity of the anode is greater than that of the cathode.
According to a further broad aspect of the present invention there is provided a non-aqueous electrolyte secondary battery. The battery comprises ari anode comprising an electrode comprising an electric conductor with a first thickness value and a pressed compact of graphitized vapor-grown carbon fibers bonded to each other by a binder, wherein said carbon fibers have a specific surface area of at most 5 m2/g and an average aspect ratio of 2-30, and said compact has a packing density of 1.2-2.0 g/cm3 measured by a method comprising cutting said electrode into a piece with a predetermined width and a predetermined length, measuring a second thickness value of said piece and the weight thereof, and calculating said packing density from said width, length, said first and second thickness values, and the weight; a cathode comprising a lithium-- 5a -containing complex oxide; and an electrolyte comprising a mixed solvent of a cyclic carbonate and a linear carbonate including a lithium salt dissolved therein.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph showing a relation between current and discharge capacity in the charging-discharging cycle tests in accordance with Examples 1, 2, 3 and 6.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
(1) Anode The anode used in the non-aqueous electrolyte secondary battery may have a compacted body comprising pressed graphitized vapor-grown carbon fibers.
Furthermore, the anode may preferably be shaped from a compacted body comprisirig an electric conductor coated with active materials, the active materials forming an active material layer on the surface of the conductor. The active materials are comprised of the graphitized vapor-grown 1i846/8 carbon fibers bonded each other by a binder.
(1-1) Graphitized Vapor-grown Carbon Fibers The graphitized vapor-grown carbon fibers used for an anode in the present invention has a specific surface area of at most 5 m2/g, preferably at most 3 m2/g, more prefera-bly at most 2 m2/g. If the specific surface area exceeds 5 m2/g, the objects of the present invention cannot be achieved, and the charge and discharge efficiency and/or cycle life is reduced to such an extent that the battery cannot be put into practice. In the other words, if the graphitized vapor-grown carbon fibers have a specific sur-face area of not more than 5 m2/g, they are advantageous compared with a plate-like graphite, a spherical graphite such as mesocarbon microbeads and a mesocarbon fiber. The reason is as follows. A graphitized vapor-grown carbon fiber has tubular networks of carbon hexagonal lattices, which networks are layered concentrically with the axis of the fiber, like growth rings of a tree. A graphitized vapor-grown carbon fiber which has been cut so as to have an aspect ratio of 2-30 has exposed parts of fracture of the graphite crystal, or the carbon lattices, only on the both ends, which lowers the fiber's function of catalyzation of the electrolysis of the solvent. On the other hand, when a plate-like graphite is used, all of the sides are the ex-posed parts of fracture of the graphite crystal and when other shapes of graphite are used, almost all of the surface are the exposed parts. Therefore, these graphites deterio-rate in safety.
Further, if the specific surface area of the graphi-tized vapor-phase grown carbon fibers is at most 5 m2/g, acceleration or catalyzation of the decomposition of the solvent with the exposed area of fracture of the graphite crystal, i.e., the fracture active reaction area of the anode can greatly be prevented.
When the specific surface area exceeds 5 m2/g, a large 2184,678 amount of white smoke to such an extent that the cathode cap is broken may be emitted if both the electrodes should make a short circuit.
To the contrary, if the specific surface area is at most 5 m2/g, an amount of smoke can greatly be decreased and the cap can be prevented from being broken.
In addition, a graphitized vapor-grown carbon fiber was used in a specific packing density, conductivity of the anode increases. Thus, addition of materials for improving conductivity, such as acetylene black, which is a high conductive carbon black having a remarkably great specific surface area is not necessary, which leads to a marked increase of safety of the battery.
The specific surface area may be determined by the BET
method.
The average aspect ratio of the graphitized vapor-phase grown carbon fibers is in the range of 2-30, preferably 3-20, more preferably 5-15. If the average aspect ratio is in the specified range, then the objects of the present inven-tion can be achieved well. In other words, the average aspect ratio exceeds 30, then there occurs such inconven-ience that the electrode cannot be formed in a sheet and a packing density of the anode is lowered, which leads to deterioration in load characteristics and safety. If the average aspect ratio is less than 2, then the specific surface area is inconveniently more than 5 m2/g.
If the average aspect ratio is in the range of 2-30, the graphitized vapor-phase grown carbon fibers are brought in contact with each other to such an extent that the elec-trode itself can have a high electric conductivity. This does not cause any great potential difference between the current collector and the surface of the electrode even when a heavy current flows at a high load. That is, uniform charging-discharging between the core and the surface of the electrode is possible, so that the charge capacity and the discharge capacity are increased. Thus, the present inven-Ll0140f0 tion can provide a non-aqueous electrolyte secondary battery exhibiting a high capacity in charging and discharging at a heavy current.
If the average aspect ratio is less than 2, the contact resistance is so large that the electric conductivity is reduced. If the average aspect ratio exceeds 30, then the packing density of the electrode is lowered, so that the electric conductivity of the electrode decreases. When the average aspect ratio is less than 2 or exceeds 30, the electric conductivity of the electrode decreases, which results in decrease in performance of the battery. As mentioned above, in conventional art, the materials for im-proving conductivity had to be added in order to make con-ductivity of the electrode greater. When the average aspect ratio is within the range, electric conductivity of the electrode itself becomes increased. Thus, addition of the materials for improving conductivity can be obviated and a non-aqueous electrolyte secondary battery with improved safety can be provided.
The graphitized vapor-grown carbon fibers are normally have an average diameter of 1-10 m, preferably 2-5 m. The average diameter in the range of 1-10 m allows the disper-sion of the fibers with a binder in an organic solvent to easily be realized and the fibers to be easily brought into contact with each other. This leads to increase in conduc-tivity of the anode with a specific packing density and to unnecessariness of adding a carbon black which is a material for improving conductivity, e.g. acetylene black. Surpris-ingly, conductivity of the anode according to the present invention is greater than that of an anode made of other graphites with addition of the materials for improving conductivity. The anode of the invention has no increase in a specific surface area by adding the materials. Both of the advantages lead to a increased safety of the non-aqueous electrolyte secondary battery.
The average aspect ratio of the graphitized vapor-grown carbon fibers is determined by taking electron microphoto-graphs of one thousand samples of the carbon fibers selected at random, measuring the length and the diameter of the selected carbon fibers, on the supposition that these carbon fibers are in a tubular form, calculating the aspect ratio from the length and the diameter for each sample, and aver-aging the calculated thousand aspect ratios. The average diameter of the carbon fibers is determined by measuring the diameter of the selected carbon fibers, and averaging the measurements of one thousand samples.
The graphitized vapor-grown carbon fibers used in the present invention have a graphite crystal structure de-veloped to a high degree and normally have a graphite net-work distance (d002), which is a distance between adjacent networks, of at most 0.338nm, preferably at most 0.337 nm, more preferably 0.3355-0.3365 nm, in view of the degree of development of a graphite network having a pattern of multi-ple hexagonal ri..ngs.
Furthermore, the graphitized vapor-grown carbon fibers used in the present invention have a thickness of the lay-ered graphite networks, i.e., a thickness of a crystallite (Lc) normally of at least 40 nm, preferably 60 nm, more preferably 80 nm.
The graphitized vapor-grown carbon fibers having a graphite network distance exceeding 0.338 nm, or a thickness of a graphite crystallite of less than 40 nm do not interca-late a sufficient amount of lithium ions and, therefore, are sometimes inconveniently used as an anode for lithium ion secondary batteries.
The graphite network distance and the thickness of the crystallite may be determined by the "Gakushinhou" method, which is proposed by Japan Society for the Promoting of Science, and is described on page 55 of "Tanso Gijutsu (Carbon Technology) I" published by Kagaku Gijutsu Shuppan-sha, 1970.
The graphitized vapor-grown carbon fibers used in the present invention has a spin density preferably in the range of at greatest 8x1018 spins/g, more preferably at greatest 7x1018 spins/g, as determined by the electron spin resonance absorption method.
The graphitized vapor-grown carbon fibers specified by the present invention may preferably be produced by fractur-ing starting graphitized vapor-grown carbon fibers in some form at a high impact strength or pressing the carbon fibers under hydrostatic pressure.
The graphitized vapor-grown carbon fibers can be pro-duced by graphitizing carbon fibers obtained by vapor-growth.
The vapor-grown carbon fibers can be produced by a vapor-growth method.
Specifically, the vapor-grown carbon fibers may be produced by the methods described in JP-A-52-107320, JP-A-57-117622, JP-A-58-156512, JP-A-58-180615, JP-A-60-185818, JP-A-60-224815, JP-A-60-231821, JP-A-61-132630, JP-A-61-132600, JP-A-61-132663, JP-A-61-225319, JP-A-61-225322, JP-A-61-225325, JP-A-61-225327, JP-A-61-225328, JP-A-61-275425, JP-A-61-282427 and JP-A-5-222619.
The graphitized vapor-grown carbon fibers may be pro-duced by heat treating the starting vapor-grown carbon fibers at a temperature in the range of not lower than 2000 C, preferably 2000 C-3000 C.
Fine starting vapor-grown carbon fibers which are not greater than 70 nm in diameter sometimes have graphite crystals or carbon lattices having sufficiently been grown when they are produced by the above-mentioned methods. The fine starting vapor-grown carbon fibers can be used for the anode without the heat treating, as well as the graphitized vapor-grown carbon fibers.
Normally, the atmosphere for the heat treatment may be an inert gas, and the heat treating time may be 5 minutes or more.
(1-2) Binder As the binder used reference may be made to a fluori-nated resin such as polyvinylidene fluoride and polytetra-fluoroethylene, a polyolefin such as polyethylene and poly-propylene, and copolymers thereof.
(1-3) Electric Conductor The electric conductor used should preferably be made of a material having a function for supporting the elec-trodes, and be resistant to chemicals and chemically and electrically stable. It may normally be made of a metal such as copper, aluminum and iron, particularly preferably copper and aluminum. Normally, copper is more preferred for the conductor of the anode and aluminum is more preferred for that of the cathode. A shape of the conductor varies upon that of the batteries, but is normally a thin sheet.
(1-4) Method of producing the Anode A method of producing the anode used in the present invention comprises firstly dispersing the graphitized vapor-grown carbon fibers together with the binder into the organic solvent, then coating the surface of the electric conductor with the resulting dispersion, and drying and pressing the coated conductor. The anode thus obtained has the active material which is applied and compacted on the surface of the electric conductor.
The solvent used is preferably a polar solvent, partic-ularly preferably a non-aqueous polar solvent such as N-methyl-2-pyrrolidone. The dispersion has a viscosity of 20-70 dPa.s, preferably 25-60 dPa.s, more preferably 35-50 dPa.s adjusted with the solvent.
When the dispersion is applied onto the electric con-ductor, the thickness and surface area of the coating vary depending upon the size of the batteries. Coating methods such as brushing, dipping, coating with a coater or spraying may properly be adopted.
L I U`tU/ U
(1-3) Electric Conductor The electric conductor used should preferably be made of a material having a function for supporting the elec-trodes, and be resistant to chemicals and chemically and electrically stable. It may normally be made of a metal such as copper, aluminum and iron, particularly preferably copper and aluminum. Normally, copper is more preferred for the conductor of the anode and aluminum is more preferred for that of the cathode. A shape of the conductor varies upon that of the batteries, but is normally a thin sheet.
(1-4) Method of producing the Anode A method of producing the anode used in the present invention comprises firstly dispersing the graphitized vapor-grown carbon fibers together with the binder into the organic solvent, then coating the surface of the electric conductor with the resulting dispersion, and drying and pressing the coated conductor. The anode thus obtained has the active material which is applied and compacted on the surface of the electric conductor.
The solvent used is preferably a polar solvent, partic-ularly preferably a non-aqueous polar solvent such as N-methyl-2-pyrrolidone. The dispersion has a viscosity of 20-70 dPa.s, preferably 25-60 dPa.s, more preferably 35-50 dPa.s adjusted with the solvent.
When the dispersion is applied onto the electric con-ductor, the thickness and surface area of the coating vary depending upon the size of the batteries. Coating methods such as brushing, dipping, coating with a coater or spraying may properly be adopted.
L I U`tU/ U
After the dispersion was applied onto the electric con-ductor, the coating is dried. The drying atmosphere may preferably be a deoxidized atmosphere containing an oxygen content of at most 100 ppm, preferably at most 80 ppm, more preferably at most 50 ppm. The deoxidized atmosphere is preferred since the oxidization of the electric conductor is inhibited even at a high temperature. The drying time in the deoxidized atmosphere is normally in the range of 5-60 minutes, preferably 10-40 minutes. The drying temperature is normally 100-180 C, preferably 120-160 C.
The dispersion-coated and dried electric conductor is pressed. The pressing apparatus used may be a pressing machine or roll pressing machine. When the roll pressing machine is used, the pressing should preferably be made with a clearance of 40-60% of the thickness of the anode active material layer.
The packing density of the compact thus pressed is in the range of 1.2-2.0 g/cm3, preferably 1.4-2.0 g/cm3, more preferably 1.5-1.8 g/cm3. If the packing density is less than 1.2 g/cm3, electric conductivity of the electrode becomes lowered and advantages of the secondary battery in load characteristics and safety cannot sufficiently be enjoyed. On the other hand, if the packing density is in the range of 1.2-2.0 g/cm3, then the object of the present invention can sufficiently be achieved.
The anode active material layer of the present inven-tion is comprised of the graphitized vapor-grown carbon fibers bonded each other by the binder. The proportion of the graphitized vapor-grown carbon fibers in the anode active material layer is normally 85-97%, preferably 87-95%, of the anode active material layer.
(2) Cathode The cathode used for the non-aqueous electrolyte sec-ondary battery of the present invention is comprised of a lithium-containing complex oxide. Preferred cathodes are formed by coating an electric conductor with an active material layer comprising a lithium-containing complex oxide and dispersed in a binder.
As the lithium-containing complex oxide reference may be made to complex oxides containing lithium and at least one metal selected from the group consisting of Groups 3B, 6A, 7A and 8 of the Periodic Table. Preferred lithium-containing complex oxide is at least one selected from the group consisting of LiMn2O4 and a lithium complex oxide as represented by the following 1o general formula:
LiNil_XMXOz wherein M is aluminum, manganese, chromium, cobalt or iron, and X is a real number of 0-1.
More preferred are lithium cobaltate (LiCoOz) lithium manganate (LiMn20q) and lithium nickelate (LiNiO2). The lithium-containing complex oxides may be used singly or in combination.
As the electrically conductive inorganic material reference may be made to, for example, acetylene black and artificial graphite, a carbon black called "KETJENBLACK"
(Registered trademark of Akzo Nobel Chemicals), and produced by KETJENBLACK INTERNATIONAL INC., or vapor-grown carbon fibers.
The binder material and the electric conductor material may be the same as used for the anode, and these materials used for the anode and the cathode may be identical to or different from each other.
The cathode may be produced by firstly dispersing the lithium-containing complex oxide as active material and the binder in the solvent, and coating the surface of the electric conductor with the resulting dispersion, and drying and pressing the coated conductor. The shape of the cathode is not particularly limited.
The solvent may be the same as used for the anode, preferably such as N-methyl-2-pyrrolidone. In dispersing the lithium-containing complex oxide into the solvent, the proportion of the lithium-containing complex oxide to the solvent is normally in the range of 50-70 wt%, preferably 55-65 wt%. The solvent used for the cathode may be the same with or different from that used for the anode.
The thickness and the surface area of the applied active material, coating method, drying method and pressing method may be the same as those in producing the anode.
The cathode active material comprises the lithium-containing complex oxide, electrically conductive inorgan-ic material and the binder. The proportion of the lithium-containing complex oxide is normally in the range of 80-95 wt%, preferably 85-92 wt% of the total weight of the cathode active material. The proportion of the electrically conduc-tive inorganic material is normally in the range of 15-3 wt %, preferably 8-4 wt% of the total weight of the cathode active material.
The conductor to be coated thereon with the dispersion is normally a sheet of a metal, preferably aluminum.
The drying method is not particularly limited and can be chosen depending upon various conditions or requirements.
The cathode is desirably formed so that it has a pack-ing density of 2.2-3.5 g/cm3, preferably 2.5-3.3 g/cm3.
(3) Production of Secondary Batteries The secondary battery of the present invention can be produced using an anode, a cathode and a non-aqueous elec-trolyte.
The non-aqueous electrolyte contains a lithium salt.
The concentration of the lithium salt is normally in the range of 0.8-2.0 mol/liter, preferably 1-1.8 mol/liter, more preferably 1-1.6 mol/liter. If the concentration of the lithium salt is within the above-mentioned range, then the object of the present invention can satisfactorily be achieved, and good cycle characteristics can advantageously be obtained at high and low temperatures.
As the lithium salt reference may be made to, for example, LiC1O4, LiPF61 LiBF4, LiAsF6 and LiCF3SO3. These salts may be used singly or in combination. Of these salts is preferably used LiPF6.
The solvent for the non-aqueous electrolyte is a cyclic carbonate/linear carbonate mixture.
The cyclic carbonate may be ethylene carbonate, propyl-ene carbonate, butylene carbonate, etc., which may be used singly or in combination. The linear carbonate may be di-methyl carbonate, diethyl carbonate, methylethyl carbonate, etc., which may be used singly or in combination. For example, such combination may be ethylene carbonate/dimethyl carbonate, ethylene carbonate/diethyl carbonate, ethylene carbonate/dimethyl carbonate/diethyl carbonate, ethylene carbonate/propylene carbonate/dimethyl carbonate, or ethyl-ene carbonate/propylene carbonate/diethyl carbonate, etc.
These mixed solvents may include such an amount of other additives that they do not damage the object of the present invention.
The mixing ratio by volume of ethylene carbonate/pro-pylene carbonate/diethyl carbonate may be in the range of 2-5/0.5-3.0/2.5-7.5. The mixing ratio by volume of ethylene carbonate/propylene carbonate/dimethyl carbonate may be in the range of 2-5/1-3/2-7.
The mix solvent containing the three or more components can satisfactorily achieve the object of the present inven-tion, and a higher ion conductivity can advantageously be obtained even at a lower temperature.
In the non-aqueous electrolyte secondary battery of the present invention, the designed capacity of the anode is adjusted to be larger than that of the cathode. The de-signed capacity may be calculated from the charging capacity per unit weight of electrode active material determined in a three electrode-type cell or coin-shaped cell with a lithium metal used as reference or opposite electrode and the total amount of the active material. Provided the designed capac-ity of the cathode is the unit, that of the anode should desirably be adjusted to over 1 to 1.6, preferably 1.05-1.4, to provide a non-aqueous electrolyte secondary battery having an improved safety.
The designed capacity of the cathode is based on the whole quantity of lithium ions contained in the cathode, the lithium ions being released from and absorbed into, when the lithium-containing complex oxide has a spinel structure.
Examples of the spinel-structured lithium-containing complex oxide are LiMnO2, etc. On the other hand, when the lithium-containing complex oxide does not have a spinel structure, the designed capacity of the cathode is based on the half quantity of lithium ions contained in the cathode.
If the whole quantity of lithium ions contained in the cathode are released from the cathode, the crystal structure of the non-spinel-structured lithium-containing complex oxide can be destroyed, which leads to deterioration of cycle characteristics of the lithium secondary battery.
Therefore cut-off voltage in charging and discharging should be adjusted accordingly. Examples of the non-spinel-structured lithium-containing complex oxide are LiCoO2, LiNiO2, etc.
As for the anode, the designed capacity of the anode may be based on a theoretical capacity, i.e. 372 mAh/g - 372 mAh per one gram of carbon in the anode, when the active materials of the anode are completely graphitized. If the active materials are not completely graphitized, the de-signed capacity of the anode is determined by measuring the capacity by a charge with a small current of not greater than 10 mAh/g to a predetermined cut-off voltage.
In using lithium nickelate (LiNiO2) as the cathode active material, use of the cyclic/linear carbonate mix solvent allows the charge and discharge efficiency in the first cycle to be reduced to 50-70% and provide a non-aque-ous electrolyte secondary battery with a reduced deteriora-tion of discharge capacity.
Furthermore, in the non-aqueous electrolyte secondary battery of the present invention, the cut-off voltage in L I 0fi-ul u charging is desirably limited to 4.1 V to provide the bat-tery with a longer life. The cut-off voltage in the charg-ing is the upper limit of voltage during the charging proc-ess.
The non-aqueous electrolyte secondary battery of the present invention may include a button-shaped battery, cylindrical battery, rectangular battery, coin-shaped bat-tery, etc.
The cylindrical battery may be produced in the follow-ing manner.
The anode and the cathode as mentioned above are wound up in a roll form putting between the anode and the cathode a separator of a porous sheet of polypropylene. The result-ing wound roll is placed in a cylindrical battery container.
An anode leading wire is welded on the bottom of the con-tainer. Then, a cathode leading wire is welded on a cathode cap comprising a safety rupture plate, closing cover and gasket. The electrolyte is placed in the container and the cathode cap is caulked on the opening of the container as anode. Thus, the battery is obtained.
The rectangular battery may be produced in the follow-ing manner. The wound roll made in the same manner as in the cylindrical battery is flattened and placed in a rectan-gular container. Alternatively, cathodes and anodes having leading wires welded thereon are alternately stacked on one another putting a separator between each cathode and each anode in a sandwich form and placed in the rectangular con-tainer.
The present invention will be illustrated below with reference to some examples and drawings.
Example 1 1) Production of Graphitized Vapor-Grown Carbon Fibers for Anode:
Vapor-grown carbon fibers having an average diameter of 2 m and an average length of 50 m were graphitized in an argon gas atmosphere at 2800 C for 30 minutes to prepare graphitized vapor-drown carbon fibers.
40 g of the graphitized vapor-grown carbon fibers was placed in a HYBRIDIZER (Registered trademark of Nara Machinery Co., Ltd.), Model NHS-1, made by K.K. Nara Kikai Seisakusho, and subjected to the high impact treatment at 4000 rpm with a peripheral speed of 50 m/s for 2 minutes.
The treated graphitized vapor-grown carbon fibers had a specific surface area of 1.4 mz/g, an average aspect ratio of 12, an average diameter of 2}.zm, a graphite network lattice distance (d002) of 0.3361 nm and a graphite crystallite thickness (Lc) of 130 nm. The graphitized vapor-grown carbon fibers after the treatment are those of the present invention.
The specific surface area and the average aspect ratio are shown in Table 1.
2) cylindrical Battery:
The anode was prepared in the following manner. 30 g of polyvinylidene fluoride (PVDF) was dissolved in 420 ml of N-methyl-2-pyrrolidone. To the resulting solution was added 270 g of the graphitized vapor-phase grown carbon fibers for the anode obtained in the above 1), which was fully dispersed with an ultrasonic disperser. A copper-made sheet of 10 pm in thickness, 3 m in length and 200 mm in width was coated with the resulting dispersion, which was dried and then pressed to form an electrode. The electrode was cut in a size of 39 mm in width and 450 mm in length. By measuring thickness and weight of the electrode, a packing density of it was calculated at 1.60 g/cm3. This electrode was used as the anode. The packing density of the anode is shown in Table 1.
The cathode was prepared in the following manner. 20 g of PVDF was dissolved in 350 ml of N-methyl-2-pyrrolidone to prepare a solution.
Then, 445 g of LiCo02r 20 g of artificial graphite and 15 g of acetylene black were ball milled to prepare a mixture.
L~6 4 6 16 The solution and the mixture were mixed and fully dispersed with an ultrasonic disperser to prepare a disper-sion.
An aluminum sheet of 20 m thick was coated with the dispersion in a surface area of 300 cm x 15 cm.
The dispersion-coated electrode was pressed on the aluminum sheet to form an electrode and the electrode was cut in a size of 38 mm in width and 430 mm in length. By measuring thickness and weight of the electrode, a packing density of it was calculated at 3..1 g/cm3. This electrode was used as the cathode.
The non-aqueous electrolyte secondary battery was produced in the following manner. The obtained cathode and anode were wound up in roll shape putting between the cath-ode and the anode a separator of a porous polypropylene sheet. The coil obtained in a roll shape was placed in a cylindrical container of 16 mm in diameter and 50 mm in height, and an anode leading wire was welded on the bottom of the container. Then, a cathode leading wire was welded on a cathode cap having a safety rupture plate, a closing cover and gasket. An electrolyte comprising a mixed solu-tion of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) with an EC/PC/DEC volume ratio of 2/1/2 containing 1 mol/l of LiPF6 dissolved therein was placed in the container. The cathode cap was caulked on the opening of the anode container. Thus, a cylindrical non-aqueous electrolyte secondary battery was obtained. A ratio of the designed capacity of the anode to that of the cathode is adjusted to 1.2 and the value is shown in Table 1.
3) Nailing Test for Cylindrical Secondary Battery:
A nail of 35 mm in length and 3 mm in diameter was penetrated at a speed of 50 mm/minute through the side wall of the cylindrical secondary battery charged at a current of 800 mA to 4.1 V. The result is shown in Table 2.
The dispersion-coated and dried electric conductor is pressed. The pressing apparatus used may be a pressing machine or roll pressing machine. When the roll pressing machine is used, the pressing should preferably be made with a clearance of 40-60% of the thickness of the anode active material layer.
The packing density of the compact thus pressed is in the range of 1.2-2.0 g/cm3, preferably 1.4-2.0 g/cm3, more preferably 1.5-1.8 g/cm3. If the packing density is less than 1.2 g/cm3, electric conductivity of the electrode becomes lowered and advantages of the secondary battery in load characteristics and safety cannot sufficiently be enjoyed. On the other hand, if the packing density is in the range of 1.2-2.0 g/cm3, then the object of the present invention can sufficiently be achieved.
The anode active material layer of the present inven-tion is comprised of the graphitized vapor-grown carbon fibers bonded each other by the binder. The proportion of the graphitized vapor-grown carbon fibers in the anode active material layer is normally 85-97%, preferably 87-95%, of the anode active material layer.
(2) Cathode The cathode used for the non-aqueous electrolyte sec-ondary battery of the present invention is comprised of a lithium-containing complex oxide. Preferred cathodes are formed by coating an electric conductor with an active material layer comprising a lithium-containing complex oxide and dispersed in a binder.
As the lithium-containing complex oxide reference may be made to complex oxides containing lithium and at least one metal selected from the group consisting of Groups 3B, 6A, 7A and 8 of the Periodic Table. Preferred lithium-containing complex oxide is at least one selected from the group consisting of LiMn2O4 and a lithium complex oxide as represented by the following 1o general formula:
LiNil_XMXOz wherein M is aluminum, manganese, chromium, cobalt or iron, and X is a real number of 0-1.
More preferred are lithium cobaltate (LiCoOz) lithium manganate (LiMn20q) and lithium nickelate (LiNiO2). The lithium-containing complex oxides may be used singly or in combination.
As the electrically conductive inorganic material reference may be made to, for example, acetylene black and artificial graphite, a carbon black called "KETJENBLACK"
(Registered trademark of Akzo Nobel Chemicals), and produced by KETJENBLACK INTERNATIONAL INC., or vapor-grown carbon fibers.
The binder material and the electric conductor material may be the same as used for the anode, and these materials used for the anode and the cathode may be identical to or different from each other.
The cathode may be produced by firstly dispersing the lithium-containing complex oxide as active material and the binder in the solvent, and coating the surface of the electric conductor with the resulting dispersion, and drying and pressing the coated conductor. The shape of the cathode is not particularly limited.
The solvent may be the same as used for the anode, preferably such as N-methyl-2-pyrrolidone. In dispersing the lithium-containing complex oxide into the solvent, the proportion of the lithium-containing complex oxide to the solvent is normally in the range of 50-70 wt%, preferably 55-65 wt%. The solvent used for the cathode may be the same with or different from that used for the anode.
The thickness and the surface area of the applied active material, coating method, drying method and pressing method may be the same as those in producing the anode.
The cathode active material comprises the lithium-containing complex oxide, electrically conductive inorgan-ic material and the binder. The proportion of the lithium-containing complex oxide is normally in the range of 80-95 wt%, preferably 85-92 wt% of the total weight of the cathode active material. The proportion of the electrically conduc-tive inorganic material is normally in the range of 15-3 wt %, preferably 8-4 wt% of the total weight of the cathode active material.
The conductor to be coated thereon with the dispersion is normally a sheet of a metal, preferably aluminum.
The drying method is not particularly limited and can be chosen depending upon various conditions or requirements.
The cathode is desirably formed so that it has a pack-ing density of 2.2-3.5 g/cm3, preferably 2.5-3.3 g/cm3.
(3) Production of Secondary Batteries The secondary battery of the present invention can be produced using an anode, a cathode and a non-aqueous elec-trolyte.
The non-aqueous electrolyte contains a lithium salt.
The concentration of the lithium salt is normally in the range of 0.8-2.0 mol/liter, preferably 1-1.8 mol/liter, more preferably 1-1.6 mol/liter. If the concentration of the lithium salt is within the above-mentioned range, then the object of the present invention can satisfactorily be achieved, and good cycle characteristics can advantageously be obtained at high and low temperatures.
As the lithium salt reference may be made to, for example, LiC1O4, LiPF61 LiBF4, LiAsF6 and LiCF3SO3. These salts may be used singly or in combination. Of these salts is preferably used LiPF6.
The solvent for the non-aqueous electrolyte is a cyclic carbonate/linear carbonate mixture.
The cyclic carbonate may be ethylene carbonate, propyl-ene carbonate, butylene carbonate, etc., which may be used singly or in combination. The linear carbonate may be di-methyl carbonate, diethyl carbonate, methylethyl carbonate, etc., which may be used singly or in combination. For example, such combination may be ethylene carbonate/dimethyl carbonate, ethylene carbonate/diethyl carbonate, ethylene carbonate/dimethyl carbonate/diethyl carbonate, ethylene carbonate/propylene carbonate/dimethyl carbonate, or ethyl-ene carbonate/propylene carbonate/diethyl carbonate, etc.
These mixed solvents may include such an amount of other additives that they do not damage the object of the present invention.
The mixing ratio by volume of ethylene carbonate/pro-pylene carbonate/diethyl carbonate may be in the range of 2-5/0.5-3.0/2.5-7.5. The mixing ratio by volume of ethylene carbonate/propylene carbonate/dimethyl carbonate may be in the range of 2-5/1-3/2-7.
The mix solvent containing the three or more components can satisfactorily achieve the object of the present inven-tion, and a higher ion conductivity can advantageously be obtained even at a lower temperature.
In the non-aqueous electrolyte secondary battery of the present invention, the designed capacity of the anode is adjusted to be larger than that of the cathode. The de-signed capacity may be calculated from the charging capacity per unit weight of electrode active material determined in a three electrode-type cell or coin-shaped cell with a lithium metal used as reference or opposite electrode and the total amount of the active material. Provided the designed capac-ity of the cathode is the unit, that of the anode should desirably be adjusted to over 1 to 1.6, preferably 1.05-1.4, to provide a non-aqueous electrolyte secondary battery having an improved safety.
The designed capacity of the cathode is based on the whole quantity of lithium ions contained in the cathode, the lithium ions being released from and absorbed into, when the lithium-containing complex oxide has a spinel structure.
Examples of the spinel-structured lithium-containing complex oxide are LiMnO2, etc. On the other hand, when the lithium-containing complex oxide does not have a spinel structure, the designed capacity of the cathode is based on the half quantity of lithium ions contained in the cathode.
If the whole quantity of lithium ions contained in the cathode are released from the cathode, the crystal structure of the non-spinel-structured lithium-containing complex oxide can be destroyed, which leads to deterioration of cycle characteristics of the lithium secondary battery.
Therefore cut-off voltage in charging and discharging should be adjusted accordingly. Examples of the non-spinel-structured lithium-containing complex oxide are LiCoO2, LiNiO2, etc.
As for the anode, the designed capacity of the anode may be based on a theoretical capacity, i.e. 372 mAh/g - 372 mAh per one gram of carbon in the anode, when the active materials of the anode are completely graphitized. If the active materials are not completely graphitized, the de-signed capacity of the anode is determined by measuring the capacity by a charge with a small current of not greater than 10 mAh/g to a predetermined cut-off voltage.
In using lithium nickelate (LiNiO2) as the cathode active material, use of the cyclic/linear carbonate mix solvent allows the charge and discharge efficiency in the first cycle to be reduced to 50-70% and provide a non-aque-ous electrolyte secondary battery with a reduced deteriora-tion of discharge capacity.
Furthermore, in the non-aqueous electrolyte secondary battery of the present invention, the cut-off voltage in L I 0fi-ul u charging is desirably limited to 4.1 V to provide the bat-tery with a longer life. The cut-off voltage in the charg-ing is the upper limit of voltage during the charging proc-ess.
The non-aqueous electrolyte secondary battery of the present invention may include a button-shaped battery, cylindrical battery, rectangular battery, coin-shaped bat-tery, etc.
The cylindrical battery may be produced in the follow-ing manner.
The anode and the cathode as mentioned above are wound up in a roll form putting between the anode and the cathode a separator of a porous sheet of polypropylene. The result-ing wound roll is placed in a cylindrical battery container.
An anode leading wire is welded on the bottom of the con-tainer. Then, a cathode leading wire is welded on a cathode cap comprising a safety rupture plate, closing cover and gasket. The electrolyte is placed in the container and the cathode cap is caulked on the opening of the container as anode. Thus, the battery is obtained.
The rectangular battery may be produced in the follow-ing manner. The wound roll made in the same manner as in the cylindrical battery is flattened and placed in a rectan-gular container. Alternatively, cathodes and anodes having leading wires welded thereon are alternately stacked on one another putting a separator between each cathode and each anode in a sandwich form and placed in the rectangular con-tainer.
The present invention will be illustrated below with reference to some examples and drawings.
Example 1 1) Production of Graphitized Vapor-Grown Carbon Fibers for Anode:
Vapor-grown carbon fibers having an average diameter of 2 m and an average length of 50 m were graphitized in an argon gas atmosphere at 2800 C for 30 minutes to prepare graphitized vapor-drown carbon fibers.
40 g of the graphitized vapor-grown carbon fibers was placed in a HYBRIDIZER (Registered trademark of Nara Machinery Co., Ltd.), Model NHS-1, made by K.K. Nara Kikai Seisakusho, and subjected to the high impact treatment at 4000 rpm with a peripheral speed of 50 m/s for 2 minutes.
The treated graphitized vapor-grown carbon fibers had a specific surface area of 1.4 mz/g, an average aspect ratio of 12, an average diameter of 2}.zm, a graphite network lattice distance (d002) of 0.3361 nm and a graphite crystallite thickness (Lc) of 130 nm. The graphitized vapor-grown carbon fibers after the treatment are those of the present invention.
The specific surface area and the average aspect ratio are shown in Table 1.
2) cylindrical Battery:
The anode was prepared in the following manner. 30 g of polyvinylidene fluoride (PVDF) was dissolved in 420 ml of N-methyl-2-pyrrolidone. To the resulting solution was added 270 g of the graphitized vapor-phase grown carbon fibers for the anode obtained in the above 1), which was fully dispersed with an ultrasonic disperser. A copper-made sheet of 10 pm in thickness, 3 m in length and 200 mm in width was coated with the resulting dispersion, which was dried and then pressed to form an electrode. The electrode was cut in a size of 39 mm in width and 450 mm in length. By measuring thickness and weight of the electrode, a packing density of it was calculated at 1.60 g/cm3. This electrode was used as the anode. The packing density of the anode is shown in Table 1.
The cathode was prepared in the following manner. 20 g of PVDF was dissolved in 350 ml of N-methyl-2-pyrrolidone to prepare a solution.
Then, 445 g of LiCo02r 20 g of artificial graphite and 15 g of acetylene black were ball milled to prepare a mixture.
L~6 4 6 16 The solution and the mixture were mixed and fully dispersed with an ultrasonic disperser to prepare a disper-sion.
An aluminum sheet of 20 m thick was coated with the dispersion in a surface area of 300 cm x 15 cm.
The dispersion-coated electrode was pressed on the aluminum sheet to form an electrode and the electrode was cut in a size of 38 mm in width and 430 mm in length. By measuring thickness and weight of the electrode, a packing density of it was calculated at 3..1 g/cm3. This electrode was used as the cathode.
The non-aqueous electrolyte secondary battery was produced in the following manner. The obtained cathode and anode were wound up in roll shape putting between the cath-ode and the anode a separator of a porous polypropylene sheet. The coil obtained in a roll shape was placed in a cylindrical container of 16 mm in diameter and 50 mm in height, and an anode leading wire was welded on the bottom of the container. Then, a cathode leading wire was welded on a cathode cap having a safety rupture plate, a closing cover and gasket. An electrolyte comprising a mixed solu-tion of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) with an EC/PC/DEC volume ratio of 2/1/2 containing 1 mol/l of LiPF6 dissolved therein was placed in the container. The cathode cap was caulked on the opening of the anode container. Thus, a cylindrical non-aqueous electrolyte secondary battery was obtained. A ratio of the designed capacity of the anode to that of the cathode is adjusted to 1.2 and the value is shown in Table 1.
3) Nailing Test for Cylindrical Secondary Battery:
A nail of 35 mm in length and 3 mm in diameter was penetrated at a speed of 50 mm/minute through the side wall of the cylindrical secondary battery charged at a current of 800 mA to 4.1 V. The result is shown in Table 2.
4) Charging-Discharging Test at Various Currents:
Charging-discharging tests were performed at a charge and discharge voltage of 2.5-4.1 V and at each current of 800 mA, 1600 mA, 2400 mA and 3200 mA. The results are shown in Table 3 and in Fig. 1.
Example 2 1) Production of Graphitized Vapor-Grown Carbon Fibers for Anode:
30 g of the same non-cut graphitized vapor-grown carbon fibers as in Example 1 were pressed at a pressure of 1000 kgf/cm2 by an hydrostatic pressing means.
The pressed fibers had a specific surface area of 2.4 m2/g, an average aspect ratio of 8, an average diameter of 2 m and a graphite network lattice distance (d002) of 0.3361 nm and a graphite crystallite thickness (Lc) of 130 nm. The pressed graphitized vapor-grown carbon fibers are those of the present invention for an anode. The specific surface area and the average aspect ratio are shown in Table 1.
2) Cylindrical Battery:
The anode was prepared in substantially the same manner as in Example 1. The packing density of the anode was 1.80 g/cm3. The packing density is shown in Table 1.
The cathode was prepared in the same manner as in Example 1, except that LiMn2O4 was used in place of LiCo02 and the packing density was 2.9 g/cm3.
The non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, using the anode above, cathode above and the same electrolyte as in Example 1. A ratio of the designed capacity of the anode to that of the cathode was adjusted to 1.1 and the value is shown in Table 1.
The same nailing test and charging-discharging test as in Example 1 were performed. The results are shown in Tables 2 and 3, and Figure 1.
Charging-discharging tests were performed at a charge and discharge voltage of 2.5-4.1 V and at each current of 800 mA, 1600 mA, 2400 mA and 3200 mA. The results are shown in Table 3 and in Fig. 1.
Example 2 1) Production of Graphitized Vapor-Grown Carbon Fibers for Anode:
30 g of the same non-cut graphitized vapor-grown carbon fibers as in Example 1 were pressed at a pressure of 1000 kgf/cm2 by an hydrostatic pressing means.
The pressed fibers had a specific surface area of 2.4 m2/g, an average aspect ratio of 8, an average diameter of 2 m and a graphite network lattice distance (d002) of 0.3361 nm and a graphite crystallite thickness (Lc) of 130 nm. The pressed graphitized vapor-grown carbon fibers are those of the present invention for an anode. The specific surface area and the average aspect ratio are shown in Table 1.
2) Cylindrical Battery:
The anode was prepared in substantially the same manner as in Example 1. The packing density of the anode was 1.80 g/cm3. The packing density is shown in Table 1.
The cathode was prepared in the same manner as in Example 1, except that LiMn2O4 was used in place of LiCo02 and the packing density was 2.9 g/cm3.
The non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, using the anode above, cathode above and the same electrolyte as in Example 1. A ratio of the designed capacity of the anode to that of the cathode was adjusted to 1.1 and the value is shown in Table 1.
The same nailing test and charging-discharging test as in Example 1 were performed. The results are shown in Tables 2 and 3, and Figure 1.
Example 3 1) Production of Graphitized Vapor-Grown Carbon Fibers for Anode:
Vapor-grown carbon fibers having an average diameter of 4}.zm and an average length of 50 pm were graphitized in an argon gas atmosphere at 2800 C for 30 minutes to prepare graphitized vapor-grown carbon fibers.
40 g of the graphitized vapor-grown carbon fibers were placed in a HYBRIDIZER (Registered trademark of Nara Machinery Co., Ltd.), Model NHS-1 made by K.K. Nara Kikai Seisakusho, and subjected to the high impact treatment at 8000 rpm with a peripheral speed of 100 m/s for 10 minutes.
The treated graphitized vapor-phase grown carbon fibers had a specific surface area of 7.0 m2/g, an average aspect ratio of 1.2, an average diameter of 4 pm, graphite network lattice distance (d002) of 0.3370 and a graphite crystallite thickness (Lc) of 60 nm. The specific surface area and the average aspect ratio are shown in Table 1.
2) Cylindrical Battery:
An anode was prepared in substantially the same manner as in Example 1. A packing density of the anode was 1.1 g/cm3.
The packing density is shown in Table 1.
A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, using the anode above, the same cathode and the same electrolyte as in Example 1. A
ratio of a designed capacity of the anode to that of the cathode was adjusted to 1.1 and the value is shown in Table 1.
The same nailing test and charging-discharging test as in Example 1 were performed. The results are shown in Tables 2 and 3, and Figure 1.
Example 4 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 3, except that the packing density of the anode was changed to 0.9 g/cm3 and the ratio of the designed capacity of the anode to that of the cathode was changed to 0.6.
A specific surface area and an average aspect ratio of the cut graphitized vapor-grown carbon fibers in this exam-ple is shown in Table 1.
The ratio of the designed capacity of the anode to that of the cathode is shown in Table 1.
The same nailing test as in Example 3 was performed.
The results are shown in Table 2.
Example 5 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that a mixture of graphitized mesocarbon microbeads (hereinbelow often referred to as MCMB) having an average particle size of 6 m and acetylene black (hereinbelow often referred to as AB) in the weight ratio of MCMB to AB being 80:10 was used in place of the graphitized vapor-grown carbon fibers.
A specific surface area of the mixture was 6.0 m2/g. A
packing density of the anode was 1.1 g/cm3. A ratio of the designed capacity of the anode to that of the cathode in the obtained non-aqueous electrolyte secondary battery was 0.8.
The values of the specific surface area, the packing density and the ratio of the designed capacity of the anode to that of the cathode are shown in Table 1.
The same nailing test as in Example 1 was performed.
The results are shown in Table 2.
Example 6 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that graphitized mesocarbon microbeads having an average particle size of 6 m were used in place of the graphitized vapor-grown carbon fibers.
The same charging-discharging test as in Example 1 was L1~4b/~
Vapor-grown carbon fibers having an average diameter of 4}.zm and an average length of 50 pm were graphitized in an argon gas atmosphere at 2800 C for 30 minutes to prepare graphitized vapor-grown carbon fibers.
40 g of the graphitized vapor-grown carbon fibers were placed in a HYBRIDIZER (Registered trademark of Nara Machinery Co., Ltd.), Model NHS-1 made by K.K. Nara Kikai Seisakusho, and subjected to the high impact treatment at 8000 rpm with a peripheral speed of 100 m/s for 10 minutes.
The treated graphitized vapor-phase grown carbon fibers had a specific surface area of 7.0 m2/g, an average aspect ratio of 1.2, an average diameter of 4 pm, graphite network lattice distance (d002) of 0.3370 and a graphite crystallite thickness (Lc) of 60 nm. The specific surface area and the average aspect ratio are shown in Table 1.
2) Cylindrical Battery:
An anode was prepared in substantially the same manner as in Example 1. A packing density of the anode was 1.1 g/cm3.
The packing density is shown in Table 1.
A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, using the anode above, the same cathode and the same electrolyte as in Example 1. A
ratio of a designed capacity of the anode to that of the cathode was adjusted to 1.1 and the value is shown in Table 1.
The same nailing test and charging-discharging test as in Example 1 were performed. The results are shown in Tables 2 and 3, and Figure 1.
Example 4 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 3, except that the packing density of the anode was changed to 0.9 g/cm3 and the ratio of the designed capacity of the anode to that of the cathode was changed to 0.6.
A specific surface area and an average aspect ratio of the cut graphitized vapor-grown carbon fibers in this exam-ple is shown in Table 1.
The ratio of the designed capacity of the anode to that of the cathode is shown in Table 1.
The same nailing test as in Example 3 was performed.
The results are shown in Table 2.
Example 5 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that a mixture of graphitized mesocarbon microbeads (hereinbelow often referred to as MCMB) having an average particle size of 6 m and acetylene black (hereinbelow often referred to as AB) in the weight ratio of MCMB to AB being 80:10 was used in place of the graphitized vapor-grown carbon fibers.
A specific surface area of the mixture was 6.0 m2/g. A
packing density of the anode was 1.1 g/cm3. A ratio of the designed capacity of the anode to that of the cathode in the obtained non-aqueous electrolyte secondary battery was 0.8.
The values of the specific surface area, the packing density and the ratio of the designed capacity of the anode to that of the cathode are shown in Table 1.
The same nailing test as in Example 1 was performed.
The results are shown in Table 2.
Example 6 A cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that graphitized mesocarbon microbeads having an average particle size of 6 m were used in place of the graphitized vapor-grown carbon fibers.
The same charging-discharging test as in Example 1 was L1~4b/~
performed. The results are shown in Table 3 and Figure 1.
Table 1 Specific Aspect Packing den- Ratio of designed surfa2e area ratio sity of anode capacity of anode (m /g) (g/cm ) to that of cathode Example 1 1.4 12 1.6 1.2 Example 2 2.4 8 1.8 1.1 Example 3 7.0 1.2 1.1 1.1 Example 4 7.0 1.2 0.9 0.6 Example 5 6.0 - 1.1 0.8 Table 2 Rupture of positive Ignition Smoking electrode cap Example 1 No No No Example 2 No No No Example 3 Yes No No Example 4 Yes Yes Yes Example 5 Yes No Yes Table 3 50th-cycle discharge capacity (mAh) Current 800 mA 1600 mA 2400 mA 3200 mA
Example 1 790 780 770 755 Example 2 780 770 760 750 Example 3 760 740 700 620 Example 6 730 700 600 420
Table 1 Specific Aspect Packing den- Ratio of designed surfa2e area ratio sity of anode capacity of anode (m /g) (g/cm ) to that of cathode Example 1 1.4 12 1.6 1.2 Example 2 2.4 8 1.8 1.1 Example 3 7.0 1.2 1.1 1.1 Example 4 7.0 1.2 0.9 0.6 Example 5 6.0 - 1.1 0.8 Table 2 Rupture of positive Ignition Smoking electrode cap Example 1 No No No Example 2 No No No Example 3 Yes No No Example 4 Yes Yes Yes Example 5 Yes No Yes Table 3 50th-cycle discharge capacity (mAh) Current 800 mA 1600 mA 2400 mA 3200 mA
Example 1 790 780 770 755 Example 2 780 770 760 750 Example 3 760 740 700 620 Example 6 730 700 600 420
Claims (7)
1. A non-aqueous electrolyte secondary battery which comprises:
an anode consisting essentially of an electrode comprising an electric conductor with a first thickness value and a pressed compact of graphitized vapor-grown carbon fibers bonded to each other by a binder, wherein said carbon fibers have an average diameter of 1-10 µm, a specific surface area of at most 5 m2/g and an average aspect ratio of 2-30, and said compact has a packing density of 1.2-2.0 g/cm3 measured by a method comprising cutting said electrode into a piece with a predetermined width and a predetermined length, measuring a second thickness value of said piece and the weight thereof, and calculating said packing density from said width, length, said first and second thickness values, and the weight;
a cathode comprising a lithium-containing complex oxide;
and an electrolyte comprising a mixed solvent of a cyclic carbonate and a linear carbonate including a lithium salt dissolved therein.
an anode consisting essentially of an electrode comprising an electric conductor with a first thickness value and a pressed compact of graphitized vapor-grown carbon fibers bonded to each other by a binder, wherein said carbon fibers have an average diameter of 1-10 µm, a specific surface area of at most 5 m2/g and an average aspect ratio of 2-30, and said compact has a packing density of 1.2-2.0 g/cm3 measured by a method comprising cutting said electrode into a piece with a predetermined width and a predetermined length, measuring a second thickness value of said piece and the weight thereof, and calculating said packing density from said width, length, said first and second thickness values, and the weight;
a cathode comprising a lithium-containing complex oxide;
and an electrolyte comprising a mixed solvent of a cyclic carbonate and a linear carbonate including a lithium salt dissolved therein.
2. A non-aqueous electrolyte secondary battery according to claim 1, wherein said lithium-containing complex oxide contains lithium and at least one metal selected from the group consisting of Groups 3B, 6A, 7A and 8 of the Periodic Table.
3. A non-aqueous electrolyte secondary battery according to claim 1, wherein said lithium-containing complex oxide is selected from the group consisting of LiMn2O4 and a lithium complex oxide represented by the following general formula:
LiNi1-X M X O2 wherein M is aluminum, manganese, chromium, cobalt or iron, and X is a real number of 0-1.
LiNi1-X M X O2 wherein M is aluminum, manganese, chromium, cobalt or iron, and X is a real number of 0-1.
4. A non-aqueous electrolyte secondary battery which comprises:
an anode consisting essentially of graphitized vapor-grown carbon fibers having an average diameter of 1-10 µm, a specific surface area of at most 5 m2/g and an average aspect ratio of 2-30, and a binder;
a cathode comprising a lithium-containing complex oxide;
and an electrolyte comprising a mixed solvent of a cyclic carbonate and a linear carbonate containing a lithium salt dissolved therein, wherein a ratio of the designed capacity of said anode to that of said cathode is from more than 1 to 1.6.
an anode consisting essentially of graphitized vapor-grown carbon fibers having an average diameter of 1-10 µm, a specific surface area of at most 5 m2/g and an average aspect ratio of 2-30, and a binder;
a cathode comprising a lithium-containing complex oxide;
and an electrolyte comprising a mixed solvent of a cyclic carbonate and a linear carbonate containing a lithium salt dissolved therein, wherein a ratio of the designed capacity of said anode to that of said cathode is from more than 1 to 1.6.
5. A non-aqueous electrolyte secondary battery according to claim 4, wherein a ratio of the designed capacity of the anode to that of the cathode is from 1.05 to 1.4.
6. A non-aqueous electrolyte secondary battery according to claim 4, wherein said lithium-containing complex oxide contains lithium and at least one metal selected from the group consisting of Groups 3B, 6A, 7A and 8 of the Periodic Table.
7. A non-aqueous electrolyte secondary battery according to claim 4, wherein said lithium-containing complex oxide is selected from the group consisting of LiMn2O4 and a lithium complex oxide represented by the following general formula:
LiNi1-X M X O2 wherein M is aluminum, manganese, chromium, cobalt or iron, and X is a real number of 0-1.
LiNi1-X M X O2 wherein M is aluminum, manganese, chromium, cobalt or iron, and X is a real number of 0-1.
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| JP8-151417 | 1996-06-12 | ||
| JP15141796A JP3538500B2 (en) | 1996-06-12 | 1996-06-12 | Non-aqueous electrolyte secondary battery |
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| US (1) | US5856043A (en) |
| JP (1) | JP3538500B2 (en) |
| KR (1) | KR100415810B1 (en) |
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| JPH0424831A (en) * | 1990-05-18 | 1992-01-28 | Fujitsu Ltd | Test device |
| JP3033175B2 (en) * | 1990-10-19 | 2000-04-17 | 松下電器産業株式会社 | Non-aqueous electrolyte secondary battery |
| JP2734822B2 (en) * | 1991-07-31 | 1998-04-02 | 日本電池株式会社 | Non-aqueous electrolyte secondary battery |
| JP3282189B2 (en) * | 1991-07-31 | 2002-05-13 | ソニー株式会社 | Non-aqueous electrolyte secondary battery |
| JP3239302B2 (en) * | 1991-12-20 | 2001-12-17 | 富士写真フイルム株式会社 | Organic electrolyte secondary battery |
| US5512393A (en) * | 1992-07-06 | 1996-04-30 | Nikkiso Company Limited | Vapor-grown and graphitized carbon fibers process for preparing same molded members thereof and composite members thereof |
| CA2099808C (en) * | 1992-07-06 | 2000-11-07 | Minoru Harada | Vapor-grown and graphitized carbon fibers, process for preparing same, molded members thereof, and composite members thereof |
| JPH0684517A (en) * | 1992-09-01 | 1994-03-25 | Japan Storage Battery Co Ltd | Nonaqueous electrolyte secondary cell |
| JPH0684542A (en) * | 1992-09-02 | 1994-03-25 | Sanyo Electric Co Ltd | Nonaqueous electrolytic solution secondary battery |
| US5639575A (en) * | 1992-12-04 | 1997-06-17 | Sony Corporation | Non-aqueous liquid electrolyte secondary battery |
| DE69422854T2 (en) * | 1993-06-03 | 2000-10-19 | Sony Corp., Tokio/Tokyo | Secondary battery with liquid non-aqueous electrolyte |
| JPH0722065A (en) * | 1993-07-01 | 1995-01-24 | Nikkiso Co Ltd | Non-aqueous lithium ion secondary battery and its electrode manufacturing method |
| US5443928A (en) * | 1994-02-18 | 1995-08-22 | Wilson Greatbatch Ltd. | Carbon electrode for a nonaqueous secondary electrochemical cell |
| EP0675555B1 (en) * | 1994-04-01 | 1999-07-28 | Kabushiki Kaisha Toshiba | Negative electrode for use in lithium secondary battery and process for producing the same |
| US5601950A (en) * | 1994-06-29 | 1997-02-11 | Sony Corporation | Non-aqueous electrolyte secondary cell |
| JP3427570B2 (en) * | 1994-10-26 | 2003-07-22 | ソニー株式会社 | Non-aqueous electrolyte secondary battery |
-
1996
- 1996-06-12 JP JP15141796A patent/JP3538500B2/en not_active Expired - Lifetime
- 1996-09-03 FR FR9610711A patent/FR2749980B1/en not_active Expired - Fee Related
- 1996-09-03 CA CA002184678A patent/CA2184678C/en not_active Expired - Fee Related
- 1996-09-04 US US08/707,379 patent/US5856043A/en not_active Expired - Fee Related
- 1996-09-04 KR KR1019960038221A patent/KR100415810B1/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH103946A (en) | 1998-01-06 |
| KR980006595A (en) | 1998-03-30 |
| FR2749980B1 (en) | 2002-11-15 |
| FR2749980A1 (en) | 1997-12-19 |
| US5856043A (en) | 1999-01-05 |
| CA2184678A1 (en) | 1997-12-13 |
| JP3538500B2 (en) | 2004-06-14 |
| KR100415810B1 (en) | 2004-05-14 |
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|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed | ||
| MKLA | Lapsed |
Effective date: 20110906 |