Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-11-23
2002-12-24
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S224000, C429S231950, C029S623100
Reexamination Certificate
active
06497979
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing an electrode for a non-aqueous electrolyte battery, and more particularly to a method for producing a non-aqueous electrolyte battery electrode which includes an electrode active material layer containing an active material having a composition of Li
x
Ni
y
M
z
O
2
(where x satisfies 0.8<x<1.5, y+z satisfies 0.8<y+z<1.2, z satisfies 0≦z<0.35, and M is at least one element selected from Co, Mg, Ca, Sr, Al, Mn and Fe) and having excellent battery characteristics and excellent physical properties of the active material layer.
TECHNICAL BACKGROUND OF THE INVENTION
Recent development in the electronic field is remarkable, and reduction in size and weight of devices such as video cameras, liquid crystal cameras, portable telephones, laptop computers, and word processors is now taking place. There are increasing needs for development of batteries with reduced size and weight and having a high energy density as power sources for these electronic devices.
Conventionally, lead batteries or nickel-cadmium batteries have been used for these electronic devices. These conventional batteries cannot sufficiently meet the needs for reduction in size and weight and achievement of a high energy density.
As batteries that meet these demands, development of non-aqueous electrolyte secondary batteries employing metal lithium or a substance capable of being doped and undoped with lithium as a negative electrode has been carried out, whereby those using a lithium cobalt oxide (LiCoO
2
) as a positive electrode material are already in practical use. This battery has a property of having a high voltage and a high energy density as compared with the conventional small secondary batteries. Therefore, they are greatly expected as a power source for driving a cordless devices, so that secondary batteries which are smaller and lighter than the conventional batteries can be fabricated.
Also, in order to achieve further reduction in size and weight and to obtain a further high energy density, development and research of active materials etc. is eagerly conducted, and a lithium nickel composite oxide LiNiO
2
is proposed as a positive electrode active material.
Here, in the electrode of a non-aqueous electrolyte battery, an electrically conductive agent is used because the active material has a poor electric conductivity except for some active materials.
For example, Japanese Laid-open Patent Publication No. 1-105,459/1989 discloses a non-aqueous electrolytic solution secondary battery including a positive electrode containing LiMn
2
O
4
and graphite as major components, a negative electrode, and a non-aqueous electrolytic solution, wherein a graphite content in the total amount of the above LiMn
2
O
4
and the graphite is 8 to 22 wt %. This means that, in using graphite as an electrically conductive agent, effects are not produced unless the graphite is added in a large amount.
Japanese Laid-open Patent Publication No. 4-215,252/1992 discloses use of a flake graphite as an electrically conductive agent for a positive electrode in a non-aqueous electrolyte secondary battery. In this way, although there are disclosures on electrically conductive agents made of graphite, the prior art fails to disclose a method of preparing a slurry.
Generally, the larger the amount of the electrically conductive agent is, the easier it is to draw out the efficiency of the active material. However, if a large amount of the electrically conductive agent is incorporated in the electrode, the amount of the active material per unit volume will decrease, so that as a result the capacity as a battery will decrease. Therefore, attempts are made to reduce the amount of the electrically conductive agent while drawing out the efficiency of the active material.
However, according to the conventional methods of preparing an electrode mixture-coating material, a large amount of the electrically conductive agent must be added in the electrode mixture in order to obtain a sufficient electrode conducting property. As a result, there arises a problem that the charge/discharge capacities per unit electrode volume or per unit electrode weight decreases.
Also, non-aqueous electrolyte secondary batteries get deteriorated in that their capacity decreases in accordance with their repeated use. One of the factors that cause such a deterioration of the batteries is considered to be that the contact of the active material and the electrically conductive agent in the electrode gets poorer, making it difficult to draw out an electricity to the outside.
In view of these facts, it is desirable to maintain a good contact of the active material and the electrically conductive agent in the electrode while reducing the amount of the electrically conductive agent of graphite as much as possible.
DISCLOSURE OF THE INVENTION
Objects of the Invention
Accordingly, the purpose of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing an electrode for a non-aqueous electrolyte battery with improved charge/discharge characteristics such as a discharge capacity and a charge/discharge cycle life and with improved physical properties of a coating film.
SUMMARY OF THE INVENTION
The present inventors have made an eager research and found out that an electrode having good charge/discharge characteristics and stable physical properties of the coating film can be obtained even with a small amount of an electrically conductive agent by wet-kneading a slurry containing an active material and the electrically conductive agent and then performing a special dispersion process in preparing an electrode active material mixture-coating material, thereby completing the present invention.
Accordingly, the present invention provides a method for producing an electrode for a non-aqueous electrolyte battery by preparing an electrode active material mixture-coating material containing at least an active material having a composition of Li
x
Ni
y
M
z
O
2
(where x satisfies 0.8<x<1.5, y+z satisfies 0.8<y+z<1.2, z satisfies 0≦z<0.35, and M is at least one element selected from Co, Mg, Ca, Sr, Al, Mn and Fe), an electrically conductive agent and a binder, and by applying said active material mixture-coating material on a collector, said method comprising the steps of wet-kneading a slurry containing at least said active material, said electrically conductive agent, said binder and an organic solvent, and then performing a dispersion process on said wet-kneaded slurry by means of a narrow-gap-type dispersing apparatus to prepare the mixture-coating material.
In the present invention, a concentration of solid components in the slurry at the wet-kneading step is preferably 70 to 90 wt %.
Also, in the present invention, the wet-kneading step is performed preferably in an atmosphere of air, nitrogen gas, or a rare gas having a moisture dew point of not more than −20° C.
According to the present invention, since the slurry is wet-kneaded and then subjected to the dispersion process by means of the narrow-gap-type dispersing apparatus in preparing the active material mixture-coating material, a sufficient electric conductivity of the electrode can be obtained with a small amount of the electrically conductive agent. As a result, an amount of the active material per unit electrode volume can be increased and large charge/discharge capacities per unit electrode volume can be obtained. Also, physical properties of a coating film can be stabilized.
DETAILED DESCRIPTION OF THE INVENTION
The active material to be used in the present invention is a lithium composite oxide represented by the general formula: Li
x
Ni
y
M
z
O
2
(where x satisfies 0.8<x<1.5, y+z satisfies 0.8<y+z<1.2, z satisfies 0≦z<0.35, and M is at least one element selected from Co, Mg, Ca, Sr, Al, Mn and Fe).
In the present invention, an average particle diameter of the above-mentioned lithium compo
Adamson David V.
Chi Ignacio
Cintra George
Iijima Tadayoshi
Kurose Shigeo
Arent Fox Kintner & Plotkin & Kahn, PLLC
Brouillette Gabrielle
Ruthkosky Mark
TDK Corporation
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