Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2000-03-30
2002-01-08
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S404000, C428S405000, C427S220000, C429S223000, C423S138000, C423S144000, C423S179000, C423S199000, C423S186000
Reexamination Certificate
active
06337132
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a layered rock salt-type oxide particle powder and a process for producing the same, and in particular to a lithium nickel-layered rock salt oxide particle powder, a lithium cobalt-layered rock salt-type oxide particle powder or a particle powder of a solid solution of these layered rock salt-type oxides, having large charging and discharging capacities with a less amount of adsorbed water in the surface of the particle and with less cycle deterioration, which is particularly useful as a positive electrode active material in a lithium battery, as well as a process for producing the same.
2. Description of the Prior Art
As the development of portable devices such as personal computers, portable telephones, etc. advances in recent years, there is an increasing demand for batteries as a power source. In particular, lithium batteries are extensively studied in various fields because lithium is a substance having a low atomic weight and a high ionization energy and can thus be expected to provide batteries with high electromotive force and high energy density.
Lithium nickel-layered rock salt-type oxides, lithium cobalt-layered rock salt-type oxides and solid solutions thereof or lithium manganese spinel oxides, which are capable of generating a high voltage of about 4 V, are extensively studied as positive electrode active materials used in the lithium battery. These compounds such as layered rock salt-type oxides and spinel oxides are obtained by mixing a starting oxide powder containing nickel, cobalt or manganese with a lithium compound powder and then calcinating the mixture. In particular, lithium cobalt-layered rock salt-type oxides, lithium nickel-layered rock salt-type oxides or solid solutions thereof are known to have higher energy density and better cycle characteristics than those of lithium manganese spinel oxides.
These positive electrode active materials in the form of powder are dispersed in a binder, coated on a metal plate such as copper, and dried for use as a positive electrode in a battery, wherein it is important that the particle-shape and particle size are well-regulated because, as the packing of the particle powder in the coating is increased, the capacity of the resulting battery is raised.
A non-aqueous organic electrolyte is used in a lithium ion battery, but it is said that if a trace of water is present in the electrolyte, the electrolyte is electrolyzed to generate a gas such as carbon dioxide (Denki Kagaku No. 11 (1994) 1023-1029), and in this case, there is a possible danger of the battery cell breakage. Further, if lithium nickel-layered rock salt-type oxides are used in such a cell, their characteristics in the battery are easily affected by the production environment such as humidity, etc., and therefore, it is said that it is necessary to control drying conditions strictly (the Japanese Society of Electric Information Communication, Technical Study Report EE98-72 (1999-01) 57-66). Generally, a powdery material has some water adsorbed in the surface thereof, but according to the above literature, it is considered that residual water in the particle powder as the positive electrode material should also be minimized.
Under the background described above, as particle powders of lithium cobalt-layered rock salt-type oxides, lithium nickel-layered rock salt-type oxides and solid solutions thereof acting as material powders for positive electrode active materials, there is a need for layered rock salt-type oxide particle powders having a narrow distribution of particle sizes with the least amount of water remaining in the surface of the particle, as well as a process for producing the same.
SUMMARY OF THE INVENTION
An object of the present invention is to provide particle powders of lithium cobalt-layered rock salt-type oxides, lithium nickel-layered rock salt-type oxides and solid solutions of these rock salt-type oxides having a narrow distribution of particle sizes with the least amount of water remaining in the surface of the particle.
Another object of the present invention is to provide a process for producing the above-mentioned particle powders of lithium cobalt-layered rock salt-type oxides, lithium nickel-layered rock salt-type oxides and solid solutions of these rock salt-type oxides.
Further objects and advantages of the present invention will become apparent for those skilled in the art from the detailed description and explanation given below.
As a result of an extensive series of studies in view of the problems described above, the present inventors have found out that a layered rock salt-type oxide particle powder whose surface has been rendered substantially hydrophobic by coating it with a coupling agent having both a hydrophobic group and a hydrophilic group, particularly a layered rock salt-type oxide powder particle obtained in a specific method, can solve the problems described above, thereby arriving at the present invention.
DETAILED DESCRIPTION OF THE INVENTION
That is, the first aspect of the present invention is directed to a lithium nickel-layered rock salt-type oxide particle powder, a lithium cobalt-layered rock salt-type oxide particle powder, or a particle powder of a solid solution of these layered rock salt-type oxides, wherein the surface of the particle is rendered hydrophobic by coating it with a coupling agent having both a hydrophobic group and a hydrophilic group.
The second aspect of the present invention is directed to a process for producing a lithium nickel-layered rock salt-type oxide particle powder, a lithium cobalt-layered rock salt-type oxide particle powder, or a particle powder of a solid solution of these layered rock salt-type oxides, which comprises the steps of:
mixing each particle powder of nickel oxide, cobalt oxide, or a solid solution of these oxides with a lithium compound,
allowing the mixed powder to incorporate 1 to 10% by weight of water and compression-molding it to form a molded body having a molding density of not less than 2 g/cm
3
,
calcining the molded body at 600 to 900° C. in an oxygen-containing gas to form a lithium nickel-layered rock salt-type oxide,
a lithium cobalt-layered rock salt-type oxide or a solid solution of these layered rock salt-type oxides,
dispersing the layered rock salt-type oxide in an organic solvent, and
adding a coupling agent to this dispersion in order to coat the surface of the particle therewith.
In a preferred embodiment of the present invention, each particle powder of nickel oxide or cobalt oxide is obtained by pyrolyzing at least one member selected from the group consisting of nickel- or cobalt-containing oxalate, acetate and carbonate at 350 to 500° C. in an oxygen-containing gas.
In a preferred embodiment of the present invention, each particle powder of the solid solution of nickel oxide and cobalt oxide is obtained by pyrolyzing at least one member selected from the group consisting of nickel- and cobalt-containing oxalate, acetate and carbonate at 350 to 500° C. in nitrogen or an inert gas.
In a preferred embodiment of the present invention, the particle powder of cobalt oxide is obtained by hydrothermal synthesis from a suspension containing cobalt hydroxide in the presence of an oxygen-containing gas.
In a preferred embodiment of the present invention, the mixing ratio of each particle powder of nickel oxide, cobalt oxide or a solid solution of these oxides and the lithium compound is in the range of 1.00 to 1.20 in terms of the molar ratio (Li/M) of lithium to nickel, cobalt, or the total of nickel and cobalt.
In a preferred embodiment of the present invention, the amount of the coupling agent for treatment is in the range of 0.1 to 5.0% by weight to the layered rock salt-type oxide particles.
Each powder of nickel oxide, cobalt oxide and a solid solution thereof (also referred to hereinafter as transition metal oxide) used in the present invention is not particularly limited. The nickel oxide and cobalt oxide are preferably those obtained by pyrolyzi
Kajiyama Akihisa
Nakamura Tatsuya
Armstrong Westerman Hattori McLeland & Naughton LLP
Kiliman Leszek
Toda Kogyo Corporation
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