Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1997-07-03
2001-07-17
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S206000
Reexamination Certificate
active
06261720
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an active material used in a positive electrode for alkaline storage batteries such as nickel-cadmium storage battery, nickel-metal hydride storage battery and the like. More particularly, it relates to an active material comprising a nickel based multi-metals oxide.
Recently, an alkaline storage battery, particularly portable sealed storage battery, has widely been used as a main power source for various portable apparatuses such as communications equipment, business machine, electrical appliance, miscellaneous goods, etc. because it is superior in well-balanced charge/discharge characteristics, cycle life and safety/reliability to other batteries. Also, it has attracted special interest as a large power source, e.g. movable main power source for electric vehicles, etc. because it is extremely superior in charge/discharge characteristic and reliability.
A typical alkaline storage battery is a nickel-cadmium storage battery with a long history. A nickel-metal hydride storage battery using a metal hydride in place of a cadmium negative electrode of this battery has recently been industrialized and a share thereof has rapidly been increased.
In order to improve the energy density and reliability, as in the past, the followings have become extremely important, that is, (1) means for filling a large amount of active materials of positive and negative electrodes in a predetermined volume by realizing light-weight, thin volume, short length and small size of a substrate and additives in an electrode, a separator, an electrolyte, a battery case and a lid member, (2) improvement of various additives and conductive materials, which enhance utilization of an active material, and (3) development of a novel active materials which exhibits high energy density under various use conditions.
Therefore, a recent technical tendency with respect to them will be described hereinafter.
As a main active material of a positive electrode in the industrial nickel-cadmium storage battery and nickel-metal hydride storage battery, a nickel oxide (NiOOH) has hitherto been used. However, as a substrate of the electrode, a network substrate having a higher porosity (e.g. foamed nickel substrate, etc.) has recently been applied in place of a sintered plaque which has been used in a conventional high performance, long cycle life sintered electrode, although the network substrate has a three-dimensional construction. As a result, an electrode wherein the foamed nickel substrate is filled with a large amount of an active material powder (hereinafter referred to as a “foamed metal type electrode”) was industrialized, so that the energy density of the nickel electrode was drastically improved (U.S. Pat. No. 4,251,603). An electrode using as a substrate a felt of nickel having the same feature as that of the foamed nickel substrate is also known.
A common advantage of using such high porosity substrate is that a simple producing method capable of directly filling a nickel oxide in the form of paste in the substrate can be used because a pore diameter can be increased unlike the conventional porous sintered substrate. On the other hand, there arose a problem that, since a powder having a large particle diameter is filled in a substrate having a pore diameter larger by far than that of the sintered substrate, influences of low conductivity of the active material powder and decrease in electrical conductivity between the active material and the substrate as a current collector are remarkably exerted, which results in deterioration of the utilization of the active material. Therefore, the conductivity has been compensated by using a method of adding Co or an oxide thereof, Ni, etc., in addition to the active material powder, that is, nickel oxide powder, or still insufficient conductivity has been compensated by incorporating metallic elements other than Ni, such as Co, etc. into the nickel oxide to form a solid solution.
It has been found that the incorporation of other metallic elements into the nickel oxide also results in remarkable improvement in charge efficiency, and incorporation of two elements Co and Cd has a remarkable effect, particularly. Thereafter, Zn having a property which is similar to that of Cd is noted and used as a substitute element for Cd and, furthermore, a solid solution material with three elements Co, Zn and Ba incorporated therein is suggested. The incorporation of other elements into the nickel oxide for the purpose of realizing high efficiency of the charge/discharge characteristic is a technique which has been known for a long time in the sintered electrode. A modification of using a solid solution nickel oxide incorporated with one or more elements selected from Mg, Ca, Ba, Ti, Zr, Mn, Co, Fe, Cu, Sc, Y, etc. is exemplified.
The incorporation of the element such as Co, Cd, Zn, etc. into the nickel oxide has an inhibitory effect on the formation of a highly oxidized compound, i.e. nickel oxyhydroxide of a &ggr; phase during overcharge, in addition to an effect of improving the charge acceptance. Therefore, the incorporation of the above metallic elements was an effective means for realizing long cycle life in the case of applying to a fragile foamed metal type electrode, unlike a fast sintered electrode because volume swelling of the nickel oxide is inhibited (U.S. Pat. No. 5,366,831).
In addition to the improvement of the active material, a shape of the active material is also improved and formed into a spherical shape which is suitable for high density filling and, therefore, it has become possible to use the active material in a practical battery.
The above method of adding Co or an oxide thereof is further improved, and a method of forming a coating layer of Co(OH)
2
on the surface of the active material powder or a method of forming a powder layer of a Co oxide has been suggested. These methods aim to realize higher efficiency of the utilization of the active material and to improve the productivity by improving the efficiency of a method of adding a conductive agent.
With the development of these techniques, the charge/discharge efficiency of the active material powder filled in a density which is higher by far than that by a conventional technique can be enhanced to the same level of an excellent sintered electrode. Therefore, the energy density of the positive electrode is remarkably increased and a nickel positive electrode having an energy density of about 600 mAh/cm
3
is put into practice at present.
On the other hand, with respect to a negative electrode, the energy density was largely improved by applying a metal hydride (AB
5
system) having high capacity density in place of a conventional cadmium negative electrode and, therefore, a negative electrode (per unit volume) having at least twice as much energy density as a positive electrode has been put into practice. In response to this, thinning of a separator, a battery case and other parts has rapidly advanced and the energy density of the battery has been increased.
However, as described above, a demand for improvement in energy density of the battery as a power source for portable apparatus has become greater and greater. In order to realize further improvement in energy density of the battery in response to such a demand, it is strongly required to realize higher energy density and higher performance of the positive electrode related to the development of a technique of realizing higher energy density of the negative electrode.
Furthermore, in view of the recent use, it is further required strongly to realize high energy density, long cycle life and safety at high temperature within the range wider than that in the case of a conventional use, particularly from about 45 to 60° C., with the variation of the use conditions of a portable electronic equipment applied as a power source. The same may be said of a large type movable main power source to which realization of small size and light-weight is required in a severe operating atmosphere.
In a foamed metal
Izumi Hidekatsu
Izumi Yoichi
Kimiya Hirokazu
Matsumoto Isao
Sakamoto Hiroyuki
Akin Gump Strauss Hauer & Feld L.L.P.
Chaney Carol
Matsushita Electric - Industrial Co., Ltd.
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