Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-08-17
2004-11-30
Weiner, Laura (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C029S623100, C429S168000, C429S169000, C429S218200, C429S206000, C427S115000
Reexamination Certificate
active
06824571
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of producing an alkaline storage battery equipped with an electrode group having alternately stacked positive electrode and negative electrode via separators, and particularly to a method of producing an alkaline storage battery, wherein the core plates of the electrodes disposed at the outermost sides of the electrode group are exposed and the electrode group is contained in a metal-made casing such that the exposed core plates are in contact with the metal-made outer casing. Further, the present invention relates to a hydrogen absorbing alloy electrode comprising an electrically conductive core plate having attached thereto mixture containing at least a hydrogen absorbing alloy powder and a binder and to the production method thereof, and also to an alkaline storage battery equipped with an electrode group formed laminating negative electrode each coated with a hydrogen absorbing alloy powder and positive electrodes via separators in a metal-made outer casing.
Recently, with the increase of small-sized potable instruments, the demand of secondary cells (storage batteries) capable of charging and discharging has been increased, and particularly, with small sizing and thinning of instruments, and increasing of necessity to use a space efficiently, the demand of a nickel-metal hydride battery obtained a large capacity battery has been rapidly increased. In the nickel-metal hydride battery of this kind, as shown in
FIG. 3
, electrode group
50
a formed by laminating a positive electrode
51
using nickel hydroxide as the active material and a negative electrode
52
using a hydrogen absorbing alloy as the active material via a separator
53
are contained together with an alkaline electrolyte in a metal-made outer casing (battery casing)
55
, and the metal-made outer casing
55
is tightly sealed to provide a nickel-metal hydride battery
50
. The negative electrode
52
is formed by coating an active material slurry made of a hydrogen absorbing alloy on both surfaces of a core plate
52
a
holding an active material.
The nickel-metal hydride battery
50
of the above-described structure has a fault that an oxygen gas generated when the positive electrode
5
is fully charged permeates through the separator
53
and diffuses in the negative electrode
52
to greatly deteriorates the negative electrode
52
. Particularly, the deterioration of the active material layer
52
b
of the negative electrode
52
, which does not face the positive electrode
51
, that is the active material layer
52
b
of the negative electrode
52
disposed at the outermost side of the electrode group
50
a
facing the metal-made outer casing
55
becomes severe. This is because the active material layer
52
b
of the negative electrode
52
disposed at the outermost side of the electrode group
50
a
does not face the positive electrode
51
, at charging, the progress of the charging reaction becomes later than the negative electrode
52
disposed at an intermediate portion. Thereby, when the positive electrode
51
is fully charged and an oxygen gas generates, the negative electrode
52
disposed at the outermost side of the electrode group
50
a
is attacked by the oxygen gas in a state the occluded amount of hydrogen is less than the negative electrode
52
disposed in an intermediate, whereby the deterioration becomes severe, and the cycle characteristics of the battery is lowered.
Also, because the active material layer
52
b
of the negative electrode
52
at the outermost side, which does not face the positive electrode
51
, becomes a region of low electrochemical activity, which does not efficiently carry out the absorbing and releasing reaction of hydrogen at charge and discharge, the active material layer
52
b
becomes an active material layer which is not substantially effectively utilized. The formation of the region, wherein the active material is not effectively utilized, in the inside of the battery casing
55
is the fault of lower the volume energy density, which is very important for the battery. Particularly, because the nickel-metal hydride battery is designed such that the electrode capacity of the negative electrode is larger than that of the positive electrode for employing a sealed structure by absorbing an oxygen gas in the negative electrode, when a portion, which is not effectively utilized, is formed, the volume energy density is considerably lowered.
Thus, as shown in
FIG. 4
, a nickel-metal hydride battery
60
is proposed in Japanese Patent Laid-Open No. 255834/1998, wherein an electrode group
60
a
having stacked a positive electrodes
61
and a negative electrodes
61
via a separator
63
is placed in a battery casing
65
, and a core plate exposed surface
62
b
is formed in such manner that an active material is disposed at the negative electrode
62
of the outermost side of the electrode group
60
a
, opposing to the positive-electrode
61
, while an active material does not exist at the side, which does not face the positive electrode
61
and opposes to the battery casing
65
. By employing such a construction, the amount of the active material disposed at the negative electrode
62
of the outermost side of the electrode group
60
a
become a half of the amount of the active material at the negative electrode of an intermediate disposed between positive electrodes
62
, and the electrode capacity thereof becomes smaller than that of the negative electrode at the intermediate.
Because the side, which is disposed at the outermost side of the electrode group and faces the battery casing, does not face the positive electrode, the side becomes a region of low electrochemical activity and does not efficiently carry out the absorbing and releasing reaction of hydrogen, but because in the nickel-metal hydride battery
60
, wherein the core plate exposure surface
62
b
is formed by removing the active material at the side disposed at the outermost side of the electrode group as described above, the active material can be dividedly added to each negative electrode
62
at an intermediate disposed between the positive electrodes
61
, the formation of the portion which is not effectively utilized can be prevented, and lowering of the volume energy density can be prevented.
Also, in the nickel-metal hydride battery, wherein the core plate exposure surface
62
b
is formed by removing the active material at the side disposed at the outermost side of the electrode group as described above, because the core plate
62
a
, which becomes the exposed surface, functions as a metal cover covering the electrode group
60
a
, the electrode group
60
a
can be easily inserted in the battery casing
65
and falling off of the active material can be effectively prevented. This is because the core plate
62
a
functions as the metal cover is an electrically conductive plate material such as a punching metal, and the like, in the casing of inserting the electrode group
60
a
into the battery casing
65
, it does not occur that the active material of the outermost side of the electrode group
60
a
falls off by being peeled off. Furthermore, because the inside surface of the battery casing
65
can be directly electrically contacted with the core plate
62
a
, the high-rate discharge characteristics can be improved.
Now, for producing the electrode having formed a core plate exposed surface, there are two kinds of methods, that is, a method, wherein at coating the active material slurry onto the core plate, the active material slurry is not coated on the side of the core plate, which becomes the core plate exposed surface, and a method, wherein after coating the active material slurry onto both surfaces of the core plate, the active material coated on the side becoming the core plate exposed surface is removed.
In the casing of forming a portion of coated the active material slurry on both surfaces of the core plate and a portion of coated the active material slurry on one surface only on one sheet of a core pla
Ikeda Yasuhiko
Imoto Teruhiko
Kondou Yasumasa
Morita Kiyoshi
Murata Tetsuyuki
Nixon & Vanderhye P.C.
Sanyo Electric Co,. Ltd.
Weiner Laura
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