Alkaline storage batteries and nickel electrodes having plurality of substrates

As a nickel electrode for alkaline storage batteries, an electrode plate comprising a plurality of electroconductive substrates and a plurality of active material layers which are alternately laminated and integrated is used, whereby mutual electric conductivity of the active material and the electroconductive substrate in the direction of thickness is increased, and active material utilization, discharge voltage characteristics as batteries and charge-discharge repetition life are improved. The nickel electrode comprises a plurality of electrode leaves each of which comprises an electroconductive substrate coated with an active material and which are laminated and integrated so that the electroconductive substrate and the active material layer are alternated with each other, a plurality of said electroconductive substrates being electrically and mechanically connected through a part of the respective electroconductive substrates, said electroconductive substrate having a thickness of 5-60 .mu.m, said active material layer coated on the electroconductive substrate having a thickness of 20-250 .mu.m.

FIELD OF THE INVENTION 
The present invention relates to alkaline storage batteries and a method of 
making nickel electrodes for the said storage batteries. 
BACKGROUND OF THE INVENTION 
With the recent spread of portable devices, a demand for high capacity, 
high performance and low cost has increased in secondary batteries 
including alkaline storage batteries. Therefore, foamed metal type 
electrodes having higher capacity density than sintered type electrodes 
have spread much as the nickel electrodes of alkaline storage batteries. 
However, the foamed metal type electrodes have the defects that the foamed 
metal as a substrate is expensive and remarkable improvement of capacity 
density is difficult owing to the structure of the foamed metal. Under the 
circumstances, pasted type electrodes comprising an inexpensive planar 
porous body as an electroconductive substrate coated with a pasted active 
material have been developed as a substitute for the foamed metal type 
electrodes. 
The planar electroconductive substrates investigated as the pasted type 
electrodes are, for example, expanded metals, screens and punching metals. 
Binders to be added to the active material paste for improving the holding 
of the active material include, for example, polyvinyl alcohol, 
carboxymethylcellulose, polyethylene, polyvinyl chloride, 
styrene-butadiene rubbers and fluororesins. 
The problems of the pasted type electrodes are insufficient contact of the 
active material with the electroconductive substrate and insufficient 
electrical conductivity because the electroconductive substrate is a 
planar porous body and not of the three-dimensional structure as of the 
foamed metal type. In order to improve the conductivity, for example, 
JP-A-56-22049 proposes to add a graphite powder, a nickel powder or a 
fiber thereof to the active material. However, when these conductive 
agents are added in such an amount as being able to obtain a capacity 
density equal to that obtained by using the foamed metal electrodes, the 
conductivity of the whole electrodes is insufficient, and active material 
utilization and discharge voltage characteristics are inferior. 
As another approach, for example, JP-A-6-314567 proposes to use an 
electroconductive substrate having a solid form, but this 
electroconductive substrate is insufficient in the contact between the 
active material and the electroconductive substrate as compared with the 
electroconductive substrates having three-dimensional structure such as 
the foamed metal. 
Therefore, unless conductive agents such as a graphite powder and a nickel 
powder are added, active material utilization is low and the electrodes 
using such electroconductive substrates are still inferior in discharge 
voltage characteristics and charge-discharge cycle life. Thus, such pasted 
electrodes have not yet been widespread. 
As aforementioned, in the case of the pasted type electrode, since the 
electroconductive substrate is planar, the contact between the active 
material and the electroconductive substrate is insufficient. 
Particularly, since the thickness of the active material layer coated on 
the electroconductive substrate is more than 300 .mu.m, the conductivity 
of the active material and the electroconductive substrate in the 
direction of thickness becomes insufficient. This is a main cause for the 
inferior active material utilization and discharge voltage characteristics 
as compared with those of foamed metal type electrodes. 
If charge and discharge are repeated using these electrode plates 
insufficient in conductivity, sufficient discharge cannot be attained and, 
hence, amount of overcharging increases in charging of the next cycle. 
Nickel hydroxide which is an active material of nickel electrode produces 
nickel oxyhydroxide of low density in an increased amount when the amount 
of overcharge increases, and this causes swelling of the plates. On the 
other hand, when the electrolyte is used in a small amount with a view 
that the gas generated from a positive plate at the time of charging is 
absorbed by a negative plate as in the case of sealed batteries, the 
nickel plate absorbs the electrolyte in an excess amount than needed with 
repetition of charging and discharging due to acceleration of swelling. 
This causes shortage of the electrolyte in separator, which gives rise to 
the problems of deterioration in both the discharge voltage and the 
capacity. 
Another problem in the pasted type electrode is that if the swelling of the 
plate increases, adhesion between the electroconductive substrate and the 
active material layer lowers, resulting in peeling off of the active 
material layer from the electroconductive substrate. 
SUMMARY OF THE INVENTION 
The main object of the present invention is to solve the above problems and 
improve the discharge voltage characteristics and the charge-discharge 
cycle life by increasing the active material utilization in pasted type 
nickel electrodes. 
The nickel electrode of the alkaline storage batteries according to the 
present invention has a structure comprising a plurality of active 
material layers each having a thickness of 20-250 .mu.m and a plurality of 
electroconductive substrates each having a thickness of 5-60 .mu.m which 
are alternately laminated into an integral form, and the electroconductive 
substrates are electrically and mechanically connected with each other 
through a part of the respective electroconductive substrates. The total 
number of the active material layers and the electroconductive substrates 
is preferably 8-12. 
The nickel electrode of the present invention can be obtained by laminating 
a plurality of electrode leaves each of which comprises the 
electroconductive substrate coated with the active material paste on one 
side or both sides with utilizing the tackiness of the paste before 
drying, thereby to integrate the active material layer and the 
electroconductive substrate, and, then, pressing the laminate to increase 
the adhesion between the electroconductive substrate and the active 
material layer with adjusting the thickness of the plate as shown in FIG. 
1. 
When they are simply laminated, current cannot be collected from the inner 
electroconductive substrates. Therefore, in order to collect a current 
uniformly from each of the electroconductive substrates, at least a part 
of the respective electroconductive substrates must be connected with each 
other. 
For example, as shown in FIG. 2, the electroconductive substrates 2 
differing in the width from each other are coated with an active material 
paste 1 at a constant width, and prepared electrode leaves. The electrode 
leaves are laminated with ends of the electrode leaves being assembled 
evenly and flat. The portion of the electroconductive substrates which is 
not coated with the active material is welded with, for example a nickel 
ribbon 3 or a nickel sheath to form a collector, and, thus, uniform 
collection of current is possible (Embodiment 1). 
Alternatively, as shown in FIG. 3, the electroconductive substrates 2 
having the same width are coated with an active material paste 1 at a 
constant width. The electrode leaves are laminated with ends of the 
electrode leaves being assembled in a stepped manner. The portion of the 
electroconductive substrates which is not coated with the active material 
is welded with, for example a nickel ribbon 3 or a nickel sheath to form a 
collector, and, thus, uniform collection of current is possible 
(Embodiment 2) 
Furthermore, as shown in FIG. 4, small holes of 0.1-1 mm in diameter are 
bored through electrode leaves which include at least one electrode leaf 
made using an electroconductive substrate having at one end a portion 
coated with no active material, and a conductive paste or conductor 8 is 
filled into the holes to connect the electroconductive substrates with 
each other, and, thus, uniform collection of current is possible 
(Embodiment 3). 
More uniform collection of current becomes possible by combining 
Embodiments 1 and 2 with Embodiment 3. 
As for the thickness of the electroconductive substrates, less than 5 .mu.m 
is not preferred because strength of the electroconductive substrate is 
low and the electroconductive substrates are broken when they are pressed 
after coated with the active material. When it is more than 60 .mu.m, the 
occupying volume increases and improvement of capacity density as a 
battery cannot be expected. 
As the electroconductive substrates, there may be used any of nickel foils, 
synthetic resin films coated with nickel on both sides and perforated 
steel sheets plated with nickel. The thickness of the nickel layer is 
preferably 2-5 .mu.m, and if it is less than 2 .mu.m, a sufficient 
conductivity cannot be secured and if it is more than 5 .mu.m, the 
capacity density decreases. As the synthetic resin films, it is necessary 
to use those which are stable in an aqueous alkali solution such as, for 
example, polypropylene, polyethylene, nylon and polytetrafluoroethylene. 
The active material and binders in which the active material is dispersed 
have no special limitation, and those known to one skilled in the art can 
be used. A conductive agents which may be added to the active material 
layer have no special limitation but such as metallic cobalt or cobalt 
oxide is preferred. 
The conductive agent to be filled into the fine holes in the Embodiment 3 
are also not limited, but a conductive paste mainly composed of Ni or a 
conductor of Ni pin is preferred. 
When the structure where a plurality of the electroconductive substrates 
are present in one plate made by lamination of them into an integral form 
is employed, there may be some fear of the electrolyte in the plate being 
ununiformly distributed. Therefore, by making fine holes of 0.1-1 mm in 
diameter through the electroconductive substrates at an opening percentage 
of 10-60%, the electrolyte can be uniformly distributed in the plate. 
However, if the opening percentage exceeds 60%, strength of the 
electroconductive substrates lowers and, hence, there is a high 
possibility of the electroconductive substrates being broken when a 
cylindrical battery is fabricated.

DESCRIPTION OF PREFERRED EMBODIMENTS 
According to the invention described in claim 1 hereinafter, the nickel 
electrode of alkaline storage battery has a structure comprising a 
plurality of active material layers each having a thickness of 20-250 
.mu.m and a plurality of electroconductive substrates each having a 
thickness of 5-60 .mu.m which are alternately laminated and integrated, 
the electroconductive substrates being electrically and mechanically 
connected with each other through a part of the respective 
electroconductive substrates. 
The invention described in claim 6 given hereinafter specifies a method for 
making a nickel electrode. When the thickness of each of the active 
material layers after making a plate is 250 .mu.m or less, the 
conductivity can be sufficiently secured by the addition of conductive 
agents such as metallic cobalt and cobalt oxide. Therefore, the nickel 
electrode is improved in active material utilization and discharge voltage 
characteristics as compared with the conventional pasted type electrodes. 
Furthermore, when at least one electroconductive substrate thicker than 
other electroconductive substrates is used, since strength of the plate is 
improved, it becomes easy to fabricate a cylindrical battery and, in 
addition, since electrical resistance of the electroconductive substrates 
decreases, discharge voltage at high rate discharge increases. The 
constituting material of this thicker electroconductive substrate may be 
the same or different from that of other electroconductive substrates. The 
electrode leaf made using the thicker electroconductive substrate may be 
placed at an optional position among a plurality of the electrode leaves, 
but preferably is placed around the center of the electrode thickness. The 
thickness of the thicker electroconductive substrate is preferably 3-10 
times that of other electroconductive substrates, and preferably 5-10 
times when only one thicker electroconductive substrate is used. 
Similarly, when fine holes of 0.1-1 mm in diameter are bored through the 
electroconductive substrates at an opening percentage of 0.5-2% and a 
conductive agent or a conductor is filled into the holes to connect the 
electroconductive substrates, the electrical resistance also decreases and 
discharge voltage at high rate discharge increases. As these holes, a part 
of the holes for distribution of the electrolyte mentioned above also can 
be used. 
Since the discharge characteristics are improved in this way, the 
overcharge decreases when charge and discharge are repeated and swelling 
of the plate can be inhibited. Furthermore, since each active material 
layer is thinner than the active material layer in the conventional pasted 
type electrode, the influence caused by swelling of the active material is 
small, peeling off from the electroconductive substrate is inhibited, and 
the cycle life in repetition of charge and discharge is improved as 
compared with conventional pasted type electrodes. 
EXAMPLE 1 
Nickel foils having holes of 0.5 mm in diameter at an opening percentage of 
20%, and having a thickness of 15 .mu.m and a width of 35.5, 36.0, 36.5 
and 37.0 mm were used as the electroconductive substrates. Both sides of 
the electroconductive substrates were coated at a thickness of 200 .mu.m 
with an active material paste of 20% in water content which was prepared 
by kneading 100 parts by weight of commercially available nickel hydroxide 
powder, 8 parts by weight of cobalt oxide powder, 15 parts by weight of 3 
wt % aqueous solution of carboxymethylcellulose, and 5 parts by weight of 
polytetrafluoroethylene dispersion (solid content 48%). The width of 
active material paste (1) coated was 35 mm, and a portion which was not 
coated with the active material was provided at one end of each 
electroconductive substrate (2). The thus coated electroconductive 
substrates were laminated with the lower ends coated with the active 
material being assembled evenly and flat as shown in FIG. 1. The laminate 
was dried at 90.degree. C., and, then was pressed so that the total 
thickness of the plate reached 0.7 mm, thereby to bond the respective 
layers. Thereafter, an Ni ribbon of 4 mm wide was welded to the portion of 
each electroconductive substrate which was not coated with the active 
material to form a current collector (3). The thus obtained plate was 
called "plate A". FIG. 1 shows a sectional view of this plate A. 
EXAMPLE 2 
Both sides of polypropylene films having holes of 0.5 mm in diameter at an 
opening percentage of 15% and having a thickness of 10 .mu.m and a width 
of 35.5, 36.0, 36.5 and 37.0 mm were coated with metallic nickel by vapor 
deposition to obtain an electroconductive substrate. The thickness of the 
nickel layer is 2.5 .mu.m. Then, plate B was made in the same manner as in 
making the plate A. In this example, a polypropylene film was used, but 
any resin films of polyethylene, nylon, polytetrafluoroethylene, etc. 
which are stable in an alkali solution can also be used. The synthetic 
resin film can be coated with nickel by electroplating or chemical plating 
in place of the vapor deposition to obtain the similar electroconductive 
substrate. 
EXAMPLES 3 and 4 
Plates C and D were made in the same manner as in EXAMPLES 1 and 2, except 
for using a nickel-plated punching metal of 36.0 mm wide in place of the 
nickel foil and nickel-coated polypropylene film of 36.0 mm wide. That is, 
the plates C and D corresponded to the plates A and B in which a thicker 
nickel-plated iron punching metal was inserted at the central part, 
respectively. The nickel-plated punching metal used had holes of 1 mm in 
diameter at an opening percentage of 50% and had a thickness of 50 .mu.m 
and a width of 36.0 mm. 
EXAMPLE 5 
Holes of 1 mm in diameter were bored at an opening percentage of 1% through 
the plate B. A conductive paste prepared by kneading 70 parts of nickel 
powder and 30 parts of a 10% aqueous carboxymethylcellulose solution was 
filled into the holes to make plate E. As a conductive paste 8, a mixture 
of Ni powder and epoxy resin may be used, and, furthermore, an Ni pin 
which is a conductor may also be used. 
Then, batteries were fabricated using the plate B, the plate D and the 
plate E and evaluated on their characteristics. 
Each plate was cut to a length of 85 mm and this was used as positive plate 
4. Moreover, negative plate 6 was made in the following manner. 
MmNi.sub.3.7 Mn.sub.0.4 Al.sub.0.3 Co.sub.0.6 which is an MmNi.sub.5 based 
hydrogen-storing alloy was ground and thereto was added a 1.5 wt % aqueous 
carboxymethylcellulose solution to prepare a paste. The paste was charged 
in a foamed nickel sheet having a porosity of 95% and a thickness of 0.8 
mm, followed by pressing it to a thickness of 0.4 mm to make an electrode. 
A 5% fluororesin dispersion was applied to the surface of the electrode. 
This pasted type hydrogen-storing alloy electrode was cut to 35 mm wide 
and 120 mm long, to which a lead plate was attached by spot welding. This 
negative plate 6 and the plate B, the plate D or the plate E between which 
a polypropylene nonwoven fabric separator subjected to hydrophilic 
treatment was inserted were rolled into a spiral and this was contained in 
case 7 to form a sealed nickel-hydrogen storage battery, which was filled 
with an electrolyte prepared by dissolving 30 g/l of lithium hydroxide in 
an aqueous potassium hydroxide solution having a specific gravity of 1.30. 
In this way, 4/5A type batteries B, D, and E of 1400 mAh in nominal 
capacity corresponding to the plates b, d and e, respectively were 
fabricated. FIG. 5 shows a sectional view of battery B. 
For comparison, battery F was fabricated in the same manner as above, using 
a nickel electrode made by coating both sides of a punching metal having a 
thickness of 70 .mu. and having holes of 2 mm in diameter at an opening 
percentage of 50% as an electroconductive substrate with the same active 
material as in EXAMPLE 1 at a thickness of 1500 .mu.m and pressing it to a 
total thickness of 0.7 mm. 
The batteries B, D, E and F were subjected to the conventional formation 
and, then, evaluated on discharge characteristics. They were charged at 
0.2 CmA for 6 hours and, then, discharged at 0.2, 1, and 3 CmA to 1.0 V. 
The results are shown in TABLE 1. 
TABLE 1 
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Active material 
utilization 
Discharging 
(Discharge Capacity 
condition 
voltage) density 
Battery 0.2 CmA 1.0 CmA 3.0 CmA 
mAh/cc 
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B 97.7% 90.9% 73.3% 630 
(1.25 V) (1.18 V) (1.10 V) 
D 98.4% 92.0% 75.2% 600 
(1.25 V) (1.20 V) (1.13 V) 
E 96.8% 91.3% 74.3% 620 
(1.25 V) (1.19 V) (1.12 V) 
F 88.8% 70.3% 49.6% 640 
(Comparative) 
(1.20 V) (1.15 V) (1.05 V) 
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From the above results, it can be seen that batteries B, D and E were 
superior to battery F in active material utilization and discharge 
voltage. Especially, the discharge voltage at a high rate discharge was 
high in batteries D and E. 
Next, batteries B, D, E and F were subjected to a cycle life test of 
carrying out the charging at 0.5 CmA at room temperature for 3 hours and 
the discharging at 1 CmA to 0.9 V. The cycle number required for the 
discharge capacity reaching 60% of the initial capacity is shown in TABLE 
2. 
TABLE 2 
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Battery Cycle number 
______________________________________ 
B 525 530 534 
D 587 590 572 
E 550 548 541 
F 203 165 186 
(Comparative) 
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From the results, it can be seen that the cycle life of batteries B, D and 
E was markedly prolonged than battery F. 
In this EXAMPLE, a hydrogen-storing alloy was used for the negative 
electrode, but the battery characteristics are similarly improved by using 
a cadmium electrode, an iron electrode and a zinc electrode as the 
negative electrode. 
As mentioned above, the nickel electrode of the alkaline storage batteries 
according to the present invention has the structure comprising a 
plurality of active material layers each having a thickness of 20-250 
.mu.m and a plurality of electroconductive substrates each having a 
thickness of 5-60 .mu.m which are alternated with each other and 
integrated, and the electroconductive substrates are electrically and 
mechanically connected through a part of the respective electroconductive 
substrates. Therefore, pasted type nickel electrodes excellent in active 
material utilization, discharge voltage characteristics and 
charge-discharge repetition characteristics are obtained.