Method of fabricating hydrogen absorbing alloy electrode

In the present invention, a hydrogen absorbing alloy containing at least nickel, cobalt and aluminum, in which the sum a of the respective abundance ratios of cobalt atoms and aluminum atoms in a portion to a depth of 30 .ANG. from its surface and the sum b of the respective abundance ratios of cobalt atoms and aluminum atoms in a bulk region inside thereof satisfy conditions of a/b.gtoreq.1.30, or a hydrogen absorbing alloy containing at least nickel, cobalt, aluminum and manganese, in which the sum A of the respective abundance ratios of cobalt atoms, aluminum atoms and manganese atoms in a portion to a depth of 30 .ANG. from its surface and the sum B of the respective abundance ratios of cobalt atoms, aluminum atoms and manganese atoms in a bulk region inside thereof satisfy conditions A/B.gtoreq.1.20 is used for a hydrogen absorbing alloy electrode in an alkali secondary battery.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a hydrogen absorbing alloy electrode used 
as a negative electrode of an alkali secondary battery such as a 
nickel-hydrogen secondary battery, a method of fabricating the hydrogen 
absorbing alloy electrode, and an alkali secondary battery using the 
hydrogen absorbing alloy electrode, and is characterized in that a 
hydrogen absorbing alloy used for the hydrogen absorbing alloy electrode 
is modified, to improve the activity in the early stages of the hydrogen 
absorbing alloy electrode and the characteristics thereof at low 
temperature. 
2. Description of the Related Art 
A nickel-hydrogen secondary battery has been conventionally known as one 
example of an alkali secondary battery. In the nickel-hydrogen secondary 
battery, a hydrogen absorbing alloy electrode using a hydrogen absorbing 
alloy has been generally used as its negative electrode. 
Examples of the hydrogen absorbing alloy used for the negative electrode 
include a hydrogen absorbing alloy having a CaCu.sub.5 -type crystal 
structure using Misch metal (Mm) which is a mixture of rare earth elements 
or a Laves type hydrogen absorbing alloy. 
In each of the hydrogen absorbing alloys, however, a coating of an oxide or 
the like is generally formed on its surface by natural oxidation, for 
example. When a hydrogen absorbing alloy electrode is fabricated using 
such a hydrogen absorbing alloy, and the hydrogen absorbing alloy 
electrode is used as a negative electrode of the nickel-hydrogen secondary 
battery, the activity in the early stages of the hydrogen absorbing alloy 
is low, and hydrogen gas is not sufficiently absorbed in the hydrogen 
absorbing alloy. As a result, some problems arise. For example, the 
capacity in the early stages of the nickel-hydrogen secondary battery is 
decreased, and the internal pressure of the battery is increased by the 
hydrogen gas. 
Therefore, in recent years, a method of immersing a hydrogen absorbing 
alloy in an acid solution such as hydrochloric acid, to remove a coating 
of an oxide on the surface of the hydrogen absorbing alloy has been 
proposed, as disclosed in Japanese Patent Laid-Open No. 225975/1993. 
When the hydrogen absorbing alloy is thus immersed in the acid solution, to 
remove the coating of the oxide on the surface of the hydrogen absorbing 
alloy, some active portions appear on the surface of the hydrogen 
absorbing alloy. 
However, the active portions thus appearing on the surface are oxidized 
again, whereby the activity in the early stages of the hydrogen absorbing 
alloy is not sufficiently improved, and the hydrogen gas is not 
sufficiently absorbed in the hydrogen absorbing alloy in the early stages. 
As a result, some problems still exist. For example, the capacity in the 
early stages of the battery is low, and the internal pressure of the 
battery is increased. 
Furthermore, in the hydrogen absorbing alloy electrode using the 
conventional hydrogen absorbing alloy, the electrochemical catalytic 
capability thereof is not sufficient, resulting in inferior discharge 
characteristics in a case where it is used under low temperature. 
SUMMARY OF THE INVENTION 
An object of the present invention is to improve, in a hydrogen absorbing 
alloy electrode used as a negative electrode of an alkali secondary 
battery such as a nickel-hydrogen secondary battery, the activity in the 
early stages of the hydrogen absorbing alloy electrode which is used as 
the negative electrode. 
Another object of the present invention is to simply obtain a hydrogen 
absorbing alloy electrode whose activity in the early stages is improved, 
resulting in increased charging and discharging characteristics. 
Still another object of the present invention is to improve, in an alkali 
secondary battery using a hydrogen absorbing alloy electrode as its 
negative electrode, the discharge capacity thereof in the early stages and 
prevent the internal pressure of the battery from being increased. 
A further object of the present invention is to obtain, in an alkali 
secondary battery using a hydrogen absorbing alloy electrode as its 
negative electrode, sufficient discharge characteristics even in a case 
where the battery is used under low temperature. 
In a first hydrogen absorbing alloy electrode according to the present 
invention, a hydrogen absorbing alloy containing at least nickel, cobalt 
and aluminum is used. Letting a be the sum of the respective abundance 
ratios of cobalt atoms and aluminum atoms in a portion to a depth of 30 
.ANG. from the surface of the hydrogen absorbing alloy, and b be the sum 
of the respective abundance ratios of cobalt atoms and aluminum atoms in a 
bulk region inside the hydrogen absorbing alloy, conditions of 
a/b.gtoreq.1.30 are satisfied. 
As in the first hydrogen absorbing alloy electrode, when more cobalt atoms 
and aluminum atoms exist on the surface of the hydrogen absorbing alloy, 
as compared with those in the bulk region inside the hydrogen absorbing 
alloy, the catalytic actions of the cobalt atoms and the aluminum atoms 
cause the activity of the hydrogen absorbing alloy electrode using the 
hydrogen absorbing alloy to be improved from the early stages and cause 
the electron conductivity thereof under low temperature to be improved. 
When the first hydrogen absorbing alloy electrode is used as a negative 
electrode of an alkali secondary battery such as a nickel-hydrogen 
secondary battery, the emission of hydrogen gas in the early stages is 
restrained, so that the capacity in the early stages of the battery is 
increased, and the internal pressure of the battery is prevented from 
being increased. Further, the electrochemical catalytic capability of the 
hydrogen absorbing alloy electrode is improved. 
In a second hydrogen absorbing alloy electrode according to the present 
invention, a hydrogen absorbing alloy containing at least nickel, cobalt, 
aluminum and manganese is used. Letting A be the sum of the respective 
abundance ratios of cobalt atoms, aluminum atoms and manganese atoms in a 
portion to a depth of 30 .ANG. from the surface of the hydrogen absorbing 
alloy, and B be the sum of the respective abundance ratios of cobalt 
atoms, aluminum atoms and manganese atoms in a bulk region inside the 
hydrogen absorbing alloy, conditions of A/B.gtoreq.1.20 are satisfied. 
As in the second hydrogen absorbing alloy electrode, when more cobalt 
atoms, aluminum atoms and manganese atoms exist on the surface of the 
hydrogen absorbing alloy, as compared with those in the bulk region inside 
the hydrogen absorbing alloy, the catalytic actions of the cobalt atoms, 
the aluminum atoms and the manganese atoms cause the activity of the 
hydrogen absorbing alloy electrode using the hydrogen absorbing alloy to 
be improved from the early stages and cause the electrochemical catalytic 
capability thereof to be improved. 
When the second hydrogen absorbing alloy electrode is used as a negative 
electrode of an alkali secondary battery such as a nickel-hydrogen 
secondary battery, the emission of hydrogen gas in the early stages is 
restrained, so that the capacity in the early stages of the battery is 
increased, and the internal pressure of the battery is prevented from 
being increased. Further, the discharge characteristics in a case where 
the battery is used under low temperature are also improved. 
In a first method of fabricating a hydrogen absorbing alloy electrode 
according to the present invention, in fabricating a hydrogen absorbing 
alloy electrode using a hydrogen absorbing alloy containing at least 
nickel, cobalt and aluminum, the hydrogen absorbing alloy is 
surface-treated in an acid solution to which 1 to 5% by weight of a cobalt 
compound and an aluminum compound per the weight of the hydrogen absorbing 
alloy are respectively added. 
When the hydrogen absorbing alloy containing nickel, cobalt and aluminum is 
thus surface-treated in the acid solution to which the cobalt compound and 
the aluminum compound are added, active portions appear on the surface of 
the hydrogen absorbing alloy, and the active portions are protected by a 
protective film composed of CoAl.sub.2 O.sub.4. Therefore, the active 
portions are prevented from being oxidized again, and the respective 
numbers of the cobalt atoms and the aluminum atoms on the surface of the 
hydrogen absorbing alloy are larger than those in the bulk region inside 
the hydrogen absorbing alloy. 
When the amounts of cobalt compound and the aluminum compound which are 
added to the acid solution are respectively set in the range of 1 to 5% by 
weight per the weight of the hydrogen absorbing alloy, the above-mentioned 
first hydrogen absorbing alloy electrode in which the relationship between 
the sum a of the respective abundance ratios of cobalt atoms and aluminum 
atoms in the portion to a depth of 30 .ANG. from the surface of the 
hydrogen absorbing alloy and the sum b of the respective abundance ratios 
of cobalt atoms and aluminum atoms in the bulk region inside the hydrogen 
absorbing alloy satisfies conditions of a/b.gtoreq.1.30 is obtained. 
When the respective amounts of the cobalt compound and the aluminum 
compound which are added to the acid solution are less than the 
above-mentioned range, the respective numbers of the cobalt atoms and the 
aluminum atoms in the portion to a depth of 30 .ANG. from the surface of 
the hydrogen absorbing alloy are decreased. On the other hand, if the 
respective amounts of the cobalt compound and the aluminum compound are 
too large, the cobalt atoms and the aluminum atoms do not remain on the 
surface of the hydrogen absorbing alloy. In either one of the cases, the 
hydrogen absorbing alloy electrode satisfying the conditions of 
a/b.gtoreq.1.30 is not obtained. 
As the cobalt compound and the aluminum compound which are added to the 
acid solution, any compounds which can be dissolved in the acid solution 
may be used. Examples of the cobalt compound include cobalt chloride and 
cobalt hydroxide (including cobalt oxyhydroxide). Examples of the aluminum 
compound include aluminum chloride and aluminum hydroxide. 
In a second method of fabricating a hydrogen absorbing alloy electrode 
according to the present invention, in fabricating a hydrogen absorbing 
alloy electrode using a hydrogen absorbing alloy containing at least 
nickel, cobalt, aluminum and manganese, the hydrogen absorbing alloy is 
surface-treated in an acid solution to which 1 to 5% by weight of an 
aluminum compound per the weight of the hydrogen absorbing alloy is added. 
When the hydrogen absorbing alloy containing nickel, cobalt, aluminum and 
manganese is thus surface-treated in the acid solution to which the 
aluminum compound is added, the respective numbers of the cobalt atoms and 
the aluminum atoms on the surface of the hydrogen absorbing alloy are 
larger than those in the bulk region inside the hydrogen absorbing alloy. 
When the amount of the aluminum compound added to the acid solution is set 
in the range of 1 to 5% by weight per the weight of the hydrogen absorbing 
alloy, the above-mentioned second hydrogen absorbing alloy electrode in 
which the relationship between the sum A of the respective abundance 
ratios of cobalt atoms, aluminum atoms and manganese atoms in the portion 
to a depth of 30 .ANG. from the surface of the hydrogen absorbing alloy 
and the sum B of the respective abundance ratios of cobalt atoms, aluminum 
atoms and the manganese atoms in the bulk region inside the hydrogen 
absorbing alloy satisfies conditions of A/B.gtoreq.1.20 is obtained. 
When the amount of the aluminum compound added to the acid solution is less 
than the above-mentioned range, the respective numbers of the cobalt 
atoms, the aluminum atoms and the manganese atoms in the portion to a 
depth of 30 .ANG. from the surface of the hydrogen absorbing alloy are 
decreased. On the other hand, if the amount of the aluminum compound is 
too large, the cobalt atoms, the aluminum atoms and the manganese atoms do 
not remain on the surface of the hydrogen absorbing alloy. In either one 
of the cases, the hydrogen absorbing alloy electrode satisfying the 
conditions of A/B.gtoreq.1.20 and a/b.gtoreq.1.3 is not obtained. 
In each of the first and second methods of fabricating the hydrogen 
absorbing alloy electrode, if the pH of the acid solution is too high, a 
coating of an oxide or the like on the surface of the hydrogen absorbing 
alloy cannot be sufficiently removed. On the other hand, if the pH of the 
acid solution is too low, an active metal in the hydrogen absorbing alloy 
is dissolved, so that the number of active portions on the surface of the 
hydrogen absorbing alloy is decreased. Therefore, the initial pH of the 
acid solution is set preferably in the range of 0.7 to 2.0. 
When the temperature of the acid solution is too high, the active metal in 
the hydrogen absorbing alloy is also dissolved, so that the number of the 
active portions on the surface of the hydrogen absorbing alloy is 
decreased. On the other hand, if the temperature of the acid solution is 
too low, the coating of the oxide or the like on the surface of the 
hydrogen absorbing alloy cannot be sufficiently removed. Therefore, the 
temperature of the acid solution is set preferably in the range of 
20.degree. C. to 70.degree. C. 
Furthermore, in treating the hydrogen absorbing alloy in the acid solution 
as described above, it is preferable that a quinone compound such as 
anthrahydroquinone is added to the acid solution. When the quinone 
compound is thus added to the acid solution, dissolved oxygen in the acid 
solution is removed, so that the active portions appearing on the surface 
of the hydrogen absorbing alloy are prevented from being oxidized again, 
and the activity in the early stages of the hydrogen absorbing alloy is 
further improved. The amount of the quinone compound added to the acid 
solution is preferably 5 ppm to 100 ppm. 
The hydrogen absorbing alloy having a CaCu.sub.5 -type crystal structure 
used in the present invention is represented by a general formula 
MmNi.sub.a Co.sub.b Al.sub.c Mn.sub.d. In the formula, Mm is a mixture of 
rare earth elements selected from La, Ce, Pr, Nd, Sm, Eu, Sc, Y, Pm, Gd, 
Tb, Gy, Ho, Er, Tm, Yb and Lu. Particularly, Mm mainly composed of a 
mixture of La, Ce, Pr, Nd and Sm is preferable. Further, a&gt;0, b&gt;0, c&gt;0, 
and d.gtoreq.0, and 4.4.ltoreq.a+b+c+d.ltoreq.5.4. 
The hydrogen absorbing alloy composed of the above-mentioned composition 
can satisfy the basic performance such as cycle characteristics and 
discharge characteristics of the alkali secondary battery. Further, 
elements Si, C, W and B may be added in the range in which the properties 
of absorbing hydrogen in the hydrogen absorbing alloy are not changed. 
In the above-mentioned composition formula, it is preferable that the 
amount a of nickel is 2.8.ltoreq.a.ltoreq.5.2, the amount b of cobalt is 
0&lt;b.ltoreq.1.4, the amount c of aluminum is 0&lt;c.ltoreq.1.2, and the amount 
d of manganese is d.ltoreq.1.2. Further, in order to increase the capacity 
of the battery, it is preferable that the amount c of aluminum is 
c.ltoreq.1.0, and the amount d of manganese is d.ltoreq.1.0. 
There and other objects, advantages and features of the invention will 
become apparent from the following description thereof taken in 
conjunction with the accompanying drawings which illustrate specific 
embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A hydrogen absorbing alloy electrode, a method of fabricating the hydrogen 
absorbing alloy electrode, and an alkali secondary battery according to 
embodiments of the present invention will be specifically described, and 
comparative examples will be taken, to make it clear that in an alkali 
secondary battery using a hydrogen absorbing alloy electrode in the 
present embodiments as its negative electrode, the internal pressure in 
the early stages of the battery is prevented from being increased, and the 
discharge characteristics thereof under low temperature are improved. The 
hydrogen absorbing alloy electrode, the method of fabricating the hydrogen 
absorbing alloy electrode, and the alkali secondary battery in the present 
invention are not particularly limited to those in the following 
embodiments, and can be embodied upon being suitably changed in the range 
in which the gist thereof is not changed. 
(Embodiments 1 to 3 and Comparative Examples 1 to 3) 
In the embodiments 1 to 3 and the comparative examples 1 to 3, Misch metal 
(Mm) which is a mixture of rare earth elements, Ni, Co, Al and Mn were so 
weighed and mixed as to have a composition of MmNi.sub.3.1 Co.sub.0.8 
Al.sub.0.4 Mn.sub.0.7, were fussed and alloyed, and were then mechanically 
ground, to obtain hydrogen absorbing allow powder. 
The surface of the hydrogen absorbing alloy powder thus obtained was 
treated in an acid solution using hydrochloric acid. 
In thus treating the surface of the hydrogen absorbing alloy powder in the 
acid solution, the initial pH of the acid solution was set to 1.0, and the 
liquid temperature thereof was set to 25.degree. C., as shown in the 
following Table 1. Further, in the embodiments 1 to 3 and the comparative 
example 1, aluminum chloride (AlCl.sub.3) and cobalt chloride (CoCl.sub.2) 
were respectively added as an aluminum compound and a cobalt compound to 
the acid solution in proportions shown in the same table, and 50 ppm of 
anthraquinone was added. In the comparative example 2, 50 ppm of only 
anthraquinone was added. In the comparative example 3, none of aluminum 
chloride, cobalt chloride and anthraquinone was added. 
A hydrogen absorbing alloy was immersed in each of the acid solutions 
adjusted in the above-mentioned manner until the pH thereof would be 7.0, 
to treat the surface of the hydrogen absorbing alloy. 
The abundance ratio of each type of atoms in a portion to a depth of 30 
.ANG. from the surface of each of the hydrogen absorbing alloys 
surface-treated in the above-mentioned manner was then measured. The 
abundance ratio of the atoms was measured using a scanning transmission 
electron micro scope and a transmission electron micro scope and by an 
energy dispersion type X-ray analysis method. The abundance ratio of the 
atoms means the ratio of the number of the atoms to the total number of 
all metallic atoms detected by the energy dispersion type X-ray analysis 
method. 
By this method, the sum a of the respective abundance ratios of Co atoms 
and Al atoms in the portion to a depth of 30 .ANG. from the surface of 
each of the hydrogen absorbing alloys was found, and the sum b of the 
respective abundance ratios of Co atoms and Al atoms in a bulk region 
inside the hydrogen absorbing alloy was similarly found, to calculate a/b. 
The results thereof were together shown in the following Table 1. 
TABLE 1 
______________________________________ 
embodiment comparative example 
1 2 3 1 2 3 
______________________________________ 
treating conditions 
of acid solution 
pH 1.0 1.0 1.0 1.0 1.0 1.0 
liquid temperature 
25 25 25 25 25 25 
(.degree. C.) 
AlCl.sub.3 (% by weight) 
1 3 5 7 0 0 
CoCl.sub.2 (% by weight) 
1 3 5 7 0 0 
anthraquinone (ppm) 
50 50 50 50 50 0 
abundance ratio of 
atoms on surface 
Co (atm/%) 19.45 21.22 22.34 
19.45 
15.56 15.56 
Al (atm/%) 2.89 3.04 3.34 2.34 1.20 1.20 
a (atm/%) 22.34 24.26 25.68 
21.79 
16.76 16.76 
abundance ratio of 
atoms inside 
b (atm/%) 17.21 17.76 18.02 
17.82 
17.01 17.01 
a/b 1.30 1.37 1.43 1.22 0.99 0.99 
______________________________________ 
As a result, in the hydrogen absorbing alloys in the embodiments 1 to 3, 
the value of a/b was not less than 1.30, which satisfied the conditions of 
the present invention. On the other hand, in the hydrogen absorbing alloy 
in the comparative example 1 which was treated using an acid solution to 
which 7% by weight, which is more than 5% by weight, of AlCl.sub.3 and 
CoCl.sub.2 were added, and the hydrogen absorbing alloy in each of the 
comparative examples 2 and 3 which was treated using an acid solution to 
which no AlCl.sub.3 and CoCl.sub.2 were added, the value of a/b was less 
than 1.30. 
20 parts by weight of a 5% solution of polyethylene oxide which is a binder 
was then added and mixed with 100 parts by weight of each of the hydrogen 
absorbing alloys surface-treated as shown in the embodiments 1 to 3 and 
the comparative examples 1 and 2, and paste was prepared, was applied to 
both surfaces of a conductive substrate composed of a punched metal 
nickel-plated and was dried at room temperature, and was then cut to 
predetermined lengths, to fabricate each of hydrogen absorbing alloy 
electrodes in the embodiments 1 to 3 and the comparative examples 1 and 2. 
Each of the hydrogen absorbing alloy electrodes thus fabricated was used as 
a negative electrode, while a sintered type nickel electrode 
conventionally used was used as a positive electrode. Further, a non-woven 
fabric having alkali resistance was used as a separator. 
As shown in FIG. 1, a separator 3 was interposed between the positive 
electrode 1 and each of the negative electrodes 2, and they were contained 
in a battery can 4 upon being spirally wound, after which 30% by weight of 
a potassium hydroxide solution was pored as an alkali electrolyte into the 
battery can 4, the battery can 4 was sealed, the positive electrode 1 was 
connected to a positive electrode cover 6 through a positive electrode 
lead 5, and the negative electrode 2 was connected to the battery can 4 
through a negative electrode lead 7, to electrically separate the battery 
can 4 and the positive electrode cover 6 by an insulating packing 8. 
A coil spring 10 was provided between the positive electrode cover 6 and a 
positive electrode external terminal 9. When the internal pressure of the 
battery was abnormally increased, the coil spring 10 was compressed, so 
that gas inside the battery was discharged into the air. 
Each of the above-mentioned nickel-hydrogen secondary batteries was so 
designed that the discharge capacity thereof would be 1000 mAh at a 
temperature of 25.degree. C. and at a current of 0.2 C. 
Each of the nickel-hydrogen secondary batteries fabricated in the 
above-mentioned manner was charged at a charging current of 0.2 C for six 
hours under room temperature (ordinary temperature), and was then 
discharged at a discharging current of 0.2 C under low temperature of 
0.degree. C., to find the initial discharge capacity of the 
nickel-hydrogen secondary battery. The results thereof were shown in the 
following Table 2. 
TABLE 2 
______________________________________ 
type of hydrogen absorbing 
initial discharge capacity 
alloy electrode (mAh) 
______________________________________ 
embodiment 1 666 
embodiment 2 669 
embodiment 3 687 
comparative example 1 
465 
comparative example 2 
445 
______________________________________ 
As apparent from the results, in each of the nickel-hydrogen secondary 
batteries respectively using as their negative electrodes the hydrogen 
absorbing alloy electrodes in the embodiments 1 to 3 using the hydrogen 
absorbing alloys in which the value of a/b was not less than 1.30, the 
initial discharge capacity thereof in a case where it was used under low 
temperature of 0.degree. C. was higher, and the discharge characteristics 
thereof under low temperature are improved, as compared with those in each 
of the nickel-hydrogen secondary batteries using as their negative 
electrodes the hydrogen absorbing alloy electrodes in the comparative 
examples 1 and 2 respectively using the hydrogen absorbing alloys in which 
the value of a/b was less than 1.30. 
(Embodiments 4 to 6 and Comparative Examples 4 to 6) 
In the embodiments 4 to 6 and the comparative examples 4 to 6, in 
surface-treating in an acid solution hydrogen absorbing alloys obtained by 
grinding in the same manner as described in the embodiments 1 to 3 and the 
comparative examples 1 to 3, the liquid temperature of the acid solution 
was set to 25.degree. C., and the amounts of AlCl.sub.3, CoCl.sub.2 and 
anthraquinone which were added to the acid solution in the embodiment 4 
were made the same as those in the embodiment 1, the amounts in the 
embodiment 5 were made the same as those in the embodiment 2, the amounts 
in the embodiment 6 were made the same as those in the embodiment 3, the 
amounts in the comparative example 4 were made the same as those in the 
comparative example 1, the amounts in the comparative example 5 were made 
the same as those in the comparative example 2, and the amounts in the 
comparative example 6 were made the same as those in the comparative 
example 3 as shown in the following Table 3, while the initial pH of the 
acid solution was changed as shown in the same table, to respectively 
surface-treat the hydrogen absorbing alloys. 
Even when the initial pH of the acid solution was changed as described 
above, the value of a/b was hardly changed, that is, the value in the 
embodiment 4 was approximately the same as that in the embodiment 1, the 
value in the embodiment 5 was approximately the same as that in the 
embodiment 2, the value in the embodiment 6 was approximately the same as 
that in the embodiment 3, the value in the comparative example 4 was 
approximately the same as that in the comparative example 1, the value in 
the comparative example 5 was approximately the same as that in the 
comparative example 2, and the value in the comparative example 6 was 
approximately the same as that in the comparative example 3. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 1 to 3 and the comparative 
examples 1 and 2 using the hydrogen absorbing alloys obtained in the 
above-mentioned manner, and nickel-hydrogen secondary batteries were 
respectively fabricated using the hydrogen absorbing alloy electrodes as 
their negative electrodes. 
The internal pressure of each of the nickel-hydrogen secondary batteries 
thus fabricated was measured while charging the battery at a current of 
1000 mA (1C) under room temperature, to measure a charging time period 
elapsed until the internal pressure of the battery reaches 10 
kgf/cm.sup.2. The charging time period was shown as the internal pressure 
characteristics in the early stages of the nickel-hydrogen secondary 
battery in the following Table 3. In determining the internal pressure 
characteristics, tests were conducted with respect to four nickel-hydrogen 
secondary batteries, and the average value thereof was shown. 
TABLE 3 
______________________________________ 
AlCl.sub.3 + internal pressure 
CoCl.sub.2 
anthraqu characteristics (min) 
(% by inone pH 
weight) (ppm) 0.5 0.7 1.0 1.5 2.0 3.0 
______________________________________ 
embodi- 
1 + 1 50 115 140 145 140 135 105 
ment 4 
embodi- 
3 + 3 50 110 140 145 145 135 100 
ment 5 
embodi- 
5 + 5 50 105 145 145 145 135 100 
ment 6 
com- 7 + 7 50 100 125 120 120 110 100 
parative 
exam- 
ple 4 
com- 0 50 95 115 120 120 110 90 
parative 
exam- 
ple 5 
com- 0 0 95 110 125 120 115 90 
parative 
exam- 
ple 6 
______________________________________ 
As apparent from the results, even when the initial pH of the acid solution 
was changed, the charging time period indicating the internal pressure 
characteristics of the battery in each of the embodiments 4 to 6 in which 
the value of a/b was not less than 1.30 as in the above-mentioned 
embodiments 1 to 3 was longer than that in each of the comparative 
examples 4 to 6 in which the value of a/b was less than 1.30 as in the 
comparative examples 1 to 3. Therefore, the emission of gas in the early 
stages was restrained, so that a sufficient discharge capacity was 
obtained from the early stages. 
In surface-treating the hydrogen absorbing alloy in the acid solution as 
described above, when the hydrogen absorbing alloy was treated in an acid 
solution whose initial pH was in the range of 0.7 to 2.0, the internal 
pressure characteristics of the nickel-hydrogen secondary battery were 
further improved. 
(Embodiments 7 to 9 and Comparative Examples 7 to 9) 
In the embodiments 7 to 9 and the comparative examples 7 to 9, in 
surface-treating in an acid solution hydrogen absorbing alloys obtained by 
grinding in the same manner as described in the embodiments 1 to 3 and the 
comparative examples 1 to 3, the initial pH of the acid solution was set 
to 1.0, and the amounts of AlCl.sub.3, CoCl.sub.2 and anthraquinone which 
were added to the acid solution in the embodiment 7 were made the same as 
those in the embodiment 1, the amounts in the embodiment 8 were made the 
same as those in the embodiment 2, the amounts in the embodiment 9 were 
made the same as those in the embodiment 3, the amounts in the comparative 
example 7 were made the same as those in the comparative example 1, the 
amounts in the comparative example 8 were made the same as those in the 
comparative example 2, and the amounts in the comparative example 9 were 
made the same as those in the comparative example 3 as shown in the 
following Table 4, while the liquid temperature of the acid solution was 
changed as shown in the same table, to respectively surface-treat the 
hydrogen absorbing alloys. 
Even when the liquid temperature of the acid solution was changed as 
described above, the value of a/b was hardly changed, that is, the value 
in the embodiment 7 was approximately the same as that in the embodiment 
1, the value in the embodiment 8 was approximately the same as that in the 
embodiment 2, the value in the embodiment 9 was approximately the same as 
that in the embodiment 3, the value in the comparative example 7 was 
approximately the same as that in the comparative example 1, the value in 
the comparative example 8 was approximately the same as that in the 
comparative example 2, and the value in the comparative example 9 was 
approximately the same as that in the comparative example 3. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 1 to 3 and the comparative 
examples 1 and 2 using the hydrogen absorbing alloys obtained in the 
above-mentioned manner, and nickel-hydrogen secondary batteries were 
respectively fabricated using the hydrogen absorbing alloy electrodes as 
their negative electrodes. 
The internal pressure in the early stages of each of the nickel-hydrogen 
secondary batteries was measured in the same manner as described above. 
The results thereof were shown in the following Table 4. 
TABLE 4 
______________________________________ 
internal pressure 
AlCl.sub.3 + characteristics (min) 
CoCl.sub.2 
anthraqu liquid temperature of acid 
(% by inone solution (.degree. C.) 
weight) (ppm) 10.0 25.0 40.0 60.0 70.0 80.0 
______________________________________ 
embodi- 
1 + 1 50 125 140 140 145 140 100 
ment 7 
embodi- 
3 + 3 50 130 145 145 145 140 115 
ment 8 
embodi- 
5 + 5 50 130 145 145 145 145 100 
ment 9 
com- 7 + 7 50 120 120 135 130 110 100 
parative 
exam- 
ple 7 
com- 0 50 115 120 120 120 110 90 
parative 
exam- 
ple 8 
com- 0 0 120 125 120 120 110 100 
parative 
exam- 
ple 9 
______________________________________ 
As apparent from the results, when the liquid temperature of the acid 
solution was in the range of 25.0.degree. C. to 70.0.degree. C., the 
charging time period indicating the internal pressure characteristics of 
the battery in each of the embodiments 7 to 9 in which the value of a/b 
was not less than 1.30 as described above was longer than that in each of 
the comparative examples 7 to 9 in which the value of a/b was less than 
1.30. Therefore, the emission of gas in the early stages was restrained, 
so that a sufficient discharge capacity was obtained from the early 
stages. 
(Embodiments 10 to 12 and Comparative Examples 10 and 11) 
In the embodiments 10 to 12 and the comparative examples 10 and 11, in 
surface-treating in an acid solution hydrogen absorbing alloys obtained by 
grinding in the same manner as described in the embodiments 1 to 3 and the 
comparative examples 1 to 3, the initial pH of the acid solution was set 
to 1.0, the liquid temperature thereof was set to 25.degree. C., and the 
amounts of AlCl.sub.3 and CoCl.sub.2 which were added to the acid solution 
in the embodiment 10 were made the same as those in the embodiment 1, the 
amounts in the embodiment 11 were made the same as those in the embodiment 
2, the amounts in the embodiment 12 were made the same as those in the 
embodiment 3, the amounts in the comparative example 10 were made the same 
as those in the comparative example 1, and the amounts in the comparative 
example 11 were made the same as those in the comparative example 2 as 
shown in the following Table 5, while the amount of anthraquinone added to 
the acid solution was changed as shown in the same table, to respectively 
surface-treat the hydrogen absorbing alloys. 
Even when the amount of anthraquinone added to the acid solution was 
changed as described above, the value of a/b was hardly changed, that is, 
the value in the embodiment 10 was approximately the same as that in the 
embodiment 1, the value in the embodiment 11 was approximately the same as 
that in the embodiment 2, the value in the embodiment 12 was approximately 
the same as that in the embodiment 3, the value in the comparative example 
10 was approximately the same as that in the comparative example 1, and 
the value in the comparative example 11 was approximately the same as that 
in the comparative example 2. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 1 to 3 and the comparative 
examples 1 and 2 using the hydrogen absorbing alloys obtained in the 
above-mentioned manner, and nickel-hydrogen secondary batteries were 
respectively fabricated using the hydrogen absorbing alloy electrodes as 
their negative electrodes. 
The internal pressure in the early stages of each of the nickel-hydrogen 
secondary batteries was measured in the same manner as described above. 
The results thereof were shown in the following Table 5. 
TABLE 5 
______________________________________ 
internal pressure characteristics 
AlCl.sub.3 + 
(min) 
COCl.sub.2 
amount of added anthraquinone 
(% by (ppm) 
weight) 
0.0 5.0 10.0 50.0 100.0 200.0 
______________________________________ 
embodiment 
1 + 1 125 140 145 145 145 105 
10 
embodiment 
3 + 3 125 140 145 145 140 105 
11 
embodiment 
5 + 5 125 145 145 145 145 105 
12 
comparative 
7 + 7 125 125 130 120 120 100 
example 10 
comparative 
0 125 110 120 120 90 80 
example 11 
______________________________________ 
As apparent from the results, when the amount of anthraquinone added to the 
acid solution was in the range of 5.0 ppm to 100.0 ppm, the charging time 
period indicating the internal pressure characteristics of the battery in 
each of the embodiments 10 to 12 in which the value of a/b was not less 
than 1.30 as described above was longer than that in each of the 
comparative examples 10 to 11 in which the value of a/b was less than 
1.30. Therefore, the emission of gas in the early stages was restrained, 
so that a sufficient discharge capacity was obtained from the early 
stages. 
(Embodiments 13 to 15 and Comparative Example 12) 
In the embodiments 13 to 15 and the comparative example 12, in 
surface-treating in an acid solution hydrogen absorbing alloys obtained by 
grinding in the same manner as described in the embodiments 1 to 3 and the 
comparative examples 1 to 3, the initial pH of the acid solution was set 
to 1.0, the liquid temperature thereof was set to 25.degree. C., and 50 
ppm of anthraquinone was added, while aluminum hydroxide {Al(OH).sub.3 } 
and cobalt chloride (CoCl.sub.2) were respectively added as an aluminum 
compound and a cobalt compound to the acid solution in proportions as 
shown in the following Table 6. 
The abundance ratio of each type of atoms in a portion to a depth of 30 
.ANG., from the surface of each of the hydrogen absorbing alloys 
surface-treated in the above-mentioned manner was measured in the same 
manner as described above. 
The sum a of the respective abundance ratios of Co atoms and Al atoms in 
the portion to a depth of 30 .ANG. from the surface of each of the 
hydrogen absorbing alloys was found, and the sum b of the respective 
abundance ratios of Co atoms and Al atoms in a bulk region inside the 
hydrogen absorbing alloy was found, to calculate a/b in the same manner as 
described above. The results were together shown in the following Table 6. 
TABLE 6 
______________________________________ 
embodi- 
embodi- 
ment ment embodiment 
comparative 
13 14 15 example 12 
______________________________________ 
treating conditions 
of acid solution 
pH 1.0 1.0 1.0 1.0 
liquid temperature 
25 25 25 25 
(.degree. C.) 
anthraquinone (ppm) 
50 50 50 50 
Al(OH).sub.3 (% by weight) 
1 3 5 7 
COCl.sub.2 (% by weight) 
1 3 5 7 
abundance ratio of 
atoms on surface 
Co (atm/%) 20.03 21.08 3.54 9.99 
Al (atm/%) 2.78 3.23 3.44 2.56 
a (atm/%) 22.81 24.31 6.98 2.55 
abundance ratio of 
atoms inside 
b (atm/%) 17.34 17.90 7.99 7.98 
a/b 1.32 1.36 1.50 1.25 
______________________________________ 
As a result, in the hydrogen absorbing alloys in the embodiments 13 to 15, 
the value of a/b was not less than 1.30, which satisfied the conditions of 
the present invention. On the other hand, in the hydrogen absorbing alloy 
in the comparative example 12 which was surface-treated using an acid 
solution to which 7% by weight, which is more than 5% by weight, of 
Al(OH).sub.3 and CoCl.sub.2 were added, the value of a/b was less than 
1.30. 
(Embodiments 16 to 18 and Comparative Example 13) 
In the embodiments 16 to 18 and the comparative example 13, in 
surface-treating in an acid solution the above-mentioned hydrogen 
absorbing alloys, the liquid temperature of the acid solution was set to 
25.degree. C., and 50 ppm of anthraquinone was added to the acid solution 
as in the embodiments 13 to 15 and the comparative example 12, and the 
amounts of Al(OH).sub.3 and CoCl.sub.2 which were added to the acid 
solution in the embodiment 16 were made the same as those in the 
embodiment 13, the amounts in the embodiment 17 were made the same as 
those in the embodiment 14, the amounts in the embodiment 18 were made the 
same as those in the embodiment 15, and the amounts in the comparative 
example 13 were made the same as those in the comparative example 12 as 
shown in the following Table 7, while the initial pH of the acid solution 
was changed as shown in the same table, to respectively surface-treat the 
hydrogen absorbing alloys. 
Even when the initial pH of the acid solution was changed as described 
above, the value of a/b was hardly changed, that is, the value in the 
embodiment 16 was approximately the same as that in the embodiment 13, the 
value in the embodiment 17 was approximately the same as that in the 
embodiment 14, the value in the embodiment 18 was approximately the same 
as that in the embodiment 15, and the value in the comparative example 13 
was approximately the same as that in the comparative example 12. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 1 to 3 and the comparative 
examples 1 and 2 using the hydrogen absorbing alloys obtained in the 
above-mentioned manner, and nickel-hydrogen secondary batteries were 
respectively fabricated using the hydrogen absorbing alloy electrodes as 
their negative electrodes. 
The internal pressure in the early stages of each of the nickel-hydrogen 
secondary batteries thus fabricated was measured in the same manner as 
described above. The results thereof were together shown in the following 
Table 7. 
TABLE 7 
______________________________________ 
AlCl.sub.3 + 
internal pressure characteristics 
COCl.sub.2 
(min) 
(% by pH 
weight) 
0.5 0.7 1.0 1.5 2.0 3.0 
______________________________________ 
embodiment 
1 + 1 110 140 145 140 135 105 
16 
embodiment 
3 + 3 115 145 150 145 140 100 
17 
embodiment 
5 + 5 115 145 145 145 135 100 
18 
comparative 
7 + 7 100 125 125 120 115 100 
example 13 
______________________________________ 
As apparent from the results, when the initial pH of the acid solution was 
changed, the charging time period indicating the internal pressure 
characteristics of the battery in each of the embodiments 16 to 18 in 
which the value of a/b was not less than 1.30 was longer than that in the 
comparative example 13 in which the value of a/b was less than 1.30. 
Therefore, the emission of gas in the early stages was restrained, so that 
a sufficient discharge capacity was obtained from the early stages. 
In surface-treating the hydrogen absorbing alloy in the acid solution as 
described above, when the hydrogen absorbing alloy was treated in an acid 
solution whose internal pH was in the range of 0.7 to 2.0, the internal 
pressure characteristics of the nickel-hydrogen secondary battery were 
further improved. 
(Embodiments 19 to 21 and Comparative Example 14) 
In the embodiments 19 to 21 and the comparative example 14, in 
surface-treating in an acid solution the above-mentioned hydrogen 
absorbing alloys, the initial pH of the acid solution was set to 1.0, and 
50 ppm of anthraquinone was added to the acid solution as in the 
embodiments 13 to 15 and the comparative example 12, and the amounts of 
Al(OH).sub.3 and CoCl.sub.2 which were added to the acid solution in the 
embodiment 19 were made the same as those in the embodiment 13, the 
amounts in the embodiment 20 were made the same as those in the embodiment 
14, the amounts in the embodiment 21 were made the same as those in the 
embodiment 15, and the amounts in the comparative example 14 were made the 
same as those in the comparative example 12 as shown in the following 
Table 8, while the liquid temperature of the acid solution was changed as 
shown in the same table, to respectively surface-treat the hydrogen 
absorbing alloys. 
Even when the liquid temperature of the acid solution was changed as 
described above, the value of a/b was hardly changed, that is, the value 
in the embodiment 19 was approximately the same as that in the embodiment 
13, the value in the embodiment 20 was approximately the same as that in 
the embodiment 14, the value in the embodiment 21 was approximately the 
same as that in the embodiment 15, and the value in the comparative 
example 14 was approximately the same as that in the comparative example 
12. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 1 to 3 and the comparative 
examples 1 and 2 using the hydrogen absorbing alloys obtained in the 
above-mentioned manner, and nickel-hydrogen secondary batteries were 
respectively fabricated using the hydrogen absorbing alloy electrodes as 
their negative electrodes. 
The internal pressure in the early stages of each of the nickel-hydrogen 
secondary batteries thus fabricated was measured in the same manner as 
described above. The results thereof were together shown in the following 
Table 8. 
TABLE 8 
______________________________________ 
internal pressure characteristics 
AlCl.sub.3 + 
(min) 
COCl.sub.2 
liquid temperature of acid solution 
(% by (.degree. C.) 
weight) 
10.0 25.0 40.0 60.0 70.0 80.0 
______________________________________ 
embodiment 
1 + 1 120 145 140 145 140 105 
19 
embodiment 
3 + 3 135 150 150 145 145 110 
20 
embodiment 
5 + 5 130 145 145 145 145 110 
21 
comparative 
7 + 7 120 125 135 135 110 105 
example 14 
______________________________________ 
As apparent from the results, when the liquid temperature of the acid 
solution was set in the range of 25.0.degree. C. to 70.0.degree. C., the 
charging time period indicating the internal pressure characteristics of 
the battery in each of the embodiments 19 to 21 in which the value of a/b 
was not less than 1.30 as described above was longer than that in the 
comparative example 14 in which the value of a/b was less than 1.30. 
Therefore, the emission of hydrogen gas in the early stages was 
restrained, so that a sufficient discharge capacity was obtained from the 
early stages. 
(Embodiments 22 to 24 and Comparative Example 15) 
In the embodiments 22 to 24 and the comparative example 15, in 
surface-treating in an acid solution the above-mentioned hydrogen 
absorbing alloys, the initial pH of the acid solution was set to 1.0, and 
the liquid temperature thereof was set to 25.degree. C. as in the 
embodiments 13 to 15 and the comparative example 12, and the amounts of 
Al(OH).sub.3 and CoCl.sub.2 which were added to the acid solution in the 
embodiment 22 were made the same as those in the embodiment 13, the 
amounts in the embodiment 23 were made the same as those in the embodiment 
14, the amounts in the embodiment 24 were made the same as those in the 
embodiment 15, and the amounts in the comparative example 15 were made the 
same as those in the comparative example 12 as shown in the following 
Table 9, while the amount of anthraquinone added to the acid solution was 
changed as shown in the same table, to respectively surface-treat the 
hydrogen absorbing alloys. 
Even when the amount of anthraquinone added to the acid solution was 
changed as described above, the value of a/b was hardly changed, that is, 
the value in the embodiment 22 was approximately the same as that in the 
embodiment 13, the value in the embodiment 23 was approximately the same 
as that in the embodiment 14, the value in the embodiment 24 was 
approximately the same as that in the embodiment 15, and the value in the 
comparative example 15 was approximately the same as that in the 
comparative example 12. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 1 to 3 and the comparative 
examples 1 and 2 using the hydrogen absorbing alloys obtained in the 
above-mentioned manner, and nickel-hydrogen secondary batteries were 
respectively fabricated using the hydrogen absorbing alloy electrodes as 
their negative electrodes. 
The internal pressure in the early stages of each of the nickel-hydrogen 
secondary batteries thus fabricated was measured in the same manner as 
described above. The results thereof were together shown in the following 
Table 9. 
TABLE 9 
______________________________________ 
internal pressure characteristics 
Al(OH) + (min) 
COCl.sub.2 amount of added anthraquinone 
(% by (ppm) 
weight) 
0.0 5.0 10.0 50.0 100.0 200.0 
______________________________________ 
embodiment 
1 + 1 120 140 145 145 145 100 
22 
embodiment 
3 + 3 125 145 150 150 145 110 
23 
embodiment 
5 + 5 120 145 145 145 145 100 
24 
comparative 
7 + 7 120 125 130 125 120 100 
example 15 
______________________________________ 
As apparent from the results, when the amount of anthraquinone added to the 
acid solution was in the range of 5.0 ppm to 100.0 ppm, the charging time 
period indicating the internal pressure characteristics of the battery in 
each of the embodiments 12 to 24 in which the value of a/b was not less 
than 1.30 as described above was longer than that in the comparative 
example 15 in which the value of a/b was less than 1.30. Therefore, the 
emission of hydrogen gas in the early stages was restrained, so that a 
sufficient discharge capacity was obtained from the early stages. 
(Embodiments 25 to 27 and Comparative Examples 16 to 18) 
In the embodiments 25 to 27 and the comparative examples 16 to 18, hydrogen 
absorbing alloy powder having a composition of MmNi.sub.3.1 Co.sub.0.8 
Al.sub.0.4 Mn.sub.0.7 was also used as described above. 
The surface of the hydrogen absorbing alloy powder was treated in an acid 
solution using hydrochloric acid. 
In thus treating the surface of the hydrogen absorbing alloy powder in the 
acid solution, the initial pH of the acid solution was set to 1.0, and the 
liquid temperature thereof was set to 25.degree. C., as shown in the 
following Table 10. Further, in the embodiments 25 to 27 and the 
comparative example 16, aluminum chloride (AlCl.sub.3) was added as an 
aluminum compound to the acid solution in a proportion as shown in the 
same table, and 50 ppm of anthraquinone was added. In the comparative 
example 17, 50 ppm of only anthraquinone was added. In the comparative 
example 18, neither of aluminum chloride and anthraquinone was added. 
A hydrogen absorbing alloy was immersed in each of the acid solutions 
adjusted in the above-mentioned manner until the pH thereof would be 7.0, 
to treat the surface of the hydrogen absorbing alloy. 
The abundance ratio of each type of atoms in a portion to a depth of 30 
.ANG. from the surface of each of the hydrogen absorbing alloys 
surface-treated in the above-mentioned manner was then measured in the 
above-mentioned manner. 
The sum A of the respective abundance ratios of Co atoms, Al atoms and Mn 
atoms in the portion to a depth of 30 .ANG. from the surface of each of 
the hydrogen absorbing alloys was found in the same manner as described 
above, and the sum B of the respective abundance ratios of Co atoms, Al 
atoms and Mn atoms in a bulk region inside the hydrogen absorbing alloy 
was found, to calculate A/B. The results thereof were together shown in 
the following Table 10. 
TABLE 10 
______________________________________ 
embodiment comparative example 
25 26 27 16 17 18 
______________________________________ 
treating conditions 
of acid solution 
pH 1.0 1.0 1.0 1.0 1.0 1.0 
liquid temperature 
25 25 25 25 25 25 
(.degree. C.) 
AlCl.sub.3 (% by weight) 
1 3 5 7 0 0 
anthraquinone (ppm) 
50 50 50 50 50 0 
abundance ratio of 
atoms on surface 
Co (atm/%) 19.87 20.98 22.12 
19.23 
15.56 15.56 
Al (atm/%) 2.23 2.56 2.98 2.34 1.20 1.20 
Mn (atm/%) 4.78 5.23 5.56 5.34 3.66 3.66 
A (atm/%) 26.88 28.77 30.66 
26.91 
20.42 20.42 
abundance ratio of 
atoms inside 
B (atm/%) 22.02 22.76 23.54 
22.98 
21.81 21.81 
A/B 1.22 1.26 1.30 1.17 0.94 0.94 
______________________________________ 
As a result, in the hydrogen absorbing alloys in the embodiments 25 to 27, 
the value of A/B was not less than 1.20, which satisfied the conditions of 
the present invention. On the other hand, in the hydrogen absorbing alloy 
in the comparative example 16 which was treated using an acid solution to 
which 7% by weight, which is more than 5% by weight, of AlCl.sub.3 was 
added, and the hydrogen absorbing alloy in each of the comparative 
examples 17 and 18 which was treated using an acid solution to which no 
AlCl.sub.3 was added, the value of A/B was less than 1.20. 
20 parts by weight of a 5% solution of polyethylene oxide which is a binder 
was added and mixed with 100 parts by weight of each of the hydrogen 
absorbing alloys surface-treated as shown in the embodiments 25 to 27 and 
the comparative examples 16 and 17, and paste was prepared, was applied to 
both surfaces of a conductive substrate composed of a punched metal 
nickel-plated and was dried at room temperature, and was then cut to 
predetermined sizes, to fabricate each of hydrogen absorbing alloy 
electrodes in the embodiments 25 to 27 and the comparative examples 16 and 
17. 
Nickel-hydrogen secondary batteries were respectively fabricated in the 
same manner as described in the embodiments 1 to 3 and the comparative 
examples 1 and 2 using the hydrogen absorbing alloy electrodes thus 
fabricated as their negative electrodes. 
Each of the nickel-hydrogen secondary batteries fabricated in the 
above-mentioned manner was charged at a charging current of 0.2 C for six 
hours under room temperature (ordinary temperature), and was then 
discharged at a discharging current of 0.2 C under low temperature of 
0.degree. C., to find the initial discharge capacity of the 
nickel-hydrogen secondary battery. The results thereof were shown in the 
following Table 11. 
TABLE 11 
______________________________________ 
type of hydrogen absorbing 
initial discharge capacity 
alloy electrode (mAh) 
______________________________________ 
embodiment 25 675 
embodiment 26 677 
embodiment 27 699 
comparative example 16 
473 
comparative example 17 
445 
______________________________________ 
As apparent from the results, in each of the nickel-hydrogen secondary 
batteries using as their negative electrodes the hydrogen absorbing alloy 
electrodes in the embodiments 25 to 27 using the hydrogen absorbing alloys 
in which the value of A/B was not less than 1.20, the initial discharge 
capacity thereof under low temperature of 0.degree. C. was higher, and the 
discharge characteristics thereof under low temperature were improved, as 
compared with those in each of the nickel-hydrogen secondary batteries 
using as their negative electrodes the hydrogen absorbing alloy electrodes 
in the comparative examples 16 and 17 respectively using the hydrogen 
absorbing alloys in which the value of A/B was less than 1.20. 
(Embodiments 28 to 30 and Comparative Examples 19 to 21) 
In the embodiments 28 to 30 and the comparative examples 19 to 21, in 
surface-treating in an acid solution the above-mentioned hydrogen 
absorbing alloys, the liquid temperature of the acid solution was set to 
25.degree. C., and the amounts of AlCl.sub.3 and anthraquinone which were 
added to the acid solution in the embodiment 28 were made the same as 
those in the embodiment 25, the amounts in the embodiment 29 were made the 
same as those in the embodiment 26, the amounts in the embodiment 30 were 
made the same as those in the embodiment 27, the amounts in the 
comparative example 19 were made the same as those in the comparative 
example 16, the amounts in the comparative example 20 were made the same 
as those in the comparative example 17, and the amount in the comparative 
example 21 were made the same as those in the comparative example 18, 
while the initial pH of the acid solution was changed as shown in the same 
table, to respectively surface-treat the hydrogen absorbing alloys. 
Even when the initial pH of the acid solution was changed as described 
above, the value of A/B was hardly changed, that is, the value in the 
embodiment 28 was approximately the same as that in the embodiment 25, the 
value in the embodiment 29 was approximately the same as that in the 
embodiment 26, the value in the embodiment 30 was approximately the same 
as that in the embodiment 27, the value in the comparative example 19 was 
approximately the same as that in the comparative example 16, the value in 
the comparative example 20 was approximately the same as that in the 
comparative example 17, and the value in the comparative example 21 was 
approximately the same as that in the comparative example 18. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 25 to 27 and the 
comparative examples 16 and 17 using the hydrogen absorbing alloys 
obtained in the above-mentioned manner, and nickel-hydrogen secondary 
batteries were respectively fabricated using the hydrogen absorbing alloy 
electrodes as their negative electrodes. 
The internal pressure of each of the nickel-hydrogen secondary batteries 
thus fabricated was measured while charging the battery at a current of 
1000 mA (1C) under room temperature, to find a charging time period 
elapsed until the internal pressure of the battery reaches 10 
kgf/cm.sup.2. The charging time period was shown as the internal pressure 
characteristics in the early stages of the nickel-hydrogen secondary 
battery in the following Table 12. In determining the internal pressure 
characteristics, tests were conducted with respect to four nickel-hydrogen 
secondary batteries, and the average value thereof was shown. 
TABLE 12 
______________________________________ 
internal pressure 
AlCl.sub.3 + 
anthraqu characteristics (min) 
(% by inone pH 
weight) (ppm) 0.5 0.7 1.0 1.5 2.0 3.0 
______________________________________ 
embodi- 
1 50 100 140 145 140 135 105 
ment 28 
embodi- 
3 50 100 135 145 145 135 100 
ment 29 
embodi- 
5 50 100 145 145 145 135 100 
ment 30 
com- 
parative 
exam- 7 50 95 125 120 120 110 90 
ple 19 
com- 0 50 95 115 120 120 110 90 
parative 
exam- 
ple 20 
com- 0 0 95 110 125 120 115 90 
parative 
exam- 
ple 21 
______________________________________ 
As apparent from the results, even when the initial pH of the acid solution 
was changed, the charging time period indicating the internal pressure 
characteristics of the battery in each of the embodiments 28 to 30 in 
which the value of A/B was not less than 1.20 as in the above-mentioned 
embodiments 25 to 27 was longer than that in each of the comparative 
examples 19 to 21 in which the value of A/B was less than 1.20 as in the 
comparative examples 16 to 17. Therefore, the emission of hydrogen gas in 
the early stages was restrained, so that a sufficient discharge capacity 
was obtained from the early stages. 
In surface-treating the hydrogen absorbing alloy in the acid solution as 
described above, when the hydrogen absorbing alloy was treated in an acid 
solution whose initial pH was in the range of 0.7 to 2.0, the internal 
pressure characteristics of each of the nickel-hydrogen secondary 
batteries were improved. 
(Embodiments 31 to 33 and Comparative Examples 22 to 24) 
In the embodiments 31 to 33 and the comparative examples 22 to 24, in 
surface-treating in an acid solution the above-mentioned hydrogen 
absorbing alloys, the initial pH of the acid solution was set to 1.0, and 
the amounts of AlCl.sub.3 and anthraquinone which were added to the acid 
solution in the embodiment 31 were made the same as those in the 
embodiment 25, the amounts in the embodiment 32 were made the same as 
those in the embodiment 26, the amounts in the embodiment 33 were made the 
same as those in the embodiment 27, the amounts in the comparative example 
22 were made the same as those in the comparative example 16, the amounts 
in the comparative example 23 were made the same as those in the 
comparative example 17, and the amounts in the comparative example 24 were 
made the same as those in the comparative example 18 as shown in the 
following Table 13, while the liquid temperature of the acid solution was 
changed as shown in the same table, to respectively surface-treat the 
hydrogen absorbing alloys. 
Even when the liquid temperature of the acid solution was changed as 
described above, the value of A/B was hardly changed, that is, the value 
in the embodiment 31 was approximately the same as that in the embodiment 
25, the value in the embodiment 32 was approximately the same as that in 
the embodiment 26, the value in the embodiment 33 was approximately the 
same as that in the embodiment 27, the value in the comparative example 22 
was approximately the same as that in the comparative example 16, the 
value in the comparative example 23 was approximately the same as that in 
the comparative example 17, and the value in the comparative example 24 
was approximately the same as that in the comparative example 18. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 25 to 27 and the 
comparative examples 16 and 17 using the hydrogen absorbing alloys 
obtained in the above-mentioned manner, and nickel-hydrogen secondary 
batteries were respectively fabricated using the hydrogen absorbing alloy 
electrodes as their negative electrodes. 
The internal pressure in the early stages of each of the nickel-hydrogen 
secondary batteries thus fabricated was measured in the same manner as 
described above. The results thereof were shown in the following Table 13. 
TABLE 13 
______________________________________ 
internal pressure 
characteristics (min) 
AlCl.sub.3 + 
anthraqu liquid temperature of acid 
(% by inone solution (.degree. C.) 
weight) (ppm) 10.0 25.0 40.0 60.0 70.0 80.0 
______________________________________ 
embodi- 
1 50 120 140 140 145 135 95 
ment 31 
embodi- 
3 50 120 145 145 145 140 95 
ment 32 
embodi- 
5 50 120 145 145 145 145 95 
ment 33 
com- 7 50 120 120 135 130 110 100 
parative 
exam- 
ple 22 
com- 0 50 115 120 120 120 110 90 
parative 
exam- 
ple 23 
com- 0 0 120 125 120 120 110 100 
parative 
exam- 
ple 24 
______________________________________ 
As apparent from the results, when the liquid temperature of the acid 
solution was set in the range of 25.0.degree. C. to 70.0.degree. C., the 
charging time period indicating the internal pressure characteristics of 
the battery in each of the embodiments 31 to 33 in which the value of A/B 
was not less than 1.20 as described above was longer than that in each of 
the comparative examples 22 to 24 in which the value of A/B was less than 
1.20. Therefore, the emission of gas in the early stages was restrained, 
so that a sufficient discharge capacity was obtained from the early 
stages. 
(Embodiments 34 to 36 and Comparative Examples 25 and 26) 
In the embodiments 34 to 36 and the comparative examples 25 to 26, in 
surface-treating in an acid solution the above-mentioned hydrogen 
absorbing alloys, the initial pH of the acid solution was set to 1.0, the 
liquid temperature thereof was set to 25.degree. C., and the amount of 
AlCl.sub.3 added to the acid solution in the embodiment 34 was made the 
same as that in the embodiment 25, the amount in the embodiment 35 was 
made the same as that in the embodiment 26, the amount in the embodiment 
37 was made the same as that in the embodiment 27, the amount in the 
comparative example 25 was made the same as that in the comparative 
example 16, and the amount in the comparative example 26 was made the same 
as that in the comparative example 17 as shown in the following Table 14, 
while the amount of anthraquninone added to the acid solution was changed 
as shown in the same table, to respectively surface-treat the hydrogen 
absorbing alloys. 
Even when the amount of anthraquinnone added to the acid solution was 
changed as described above, the value of A/B was hardly changed, that is, 
the value in the embodiment 34 was approximately the same as that in the 
embodiment 25, the value in the embodiment 35 was approximately the same 
as that in the embodiment 26, the value in the embodiment 36 was 
approximately the same as that in the embodiment 27, the value in the 
comparative example 25 was approximately the same as that in the 
comparative example 16, and the value in the comparative example 26 was 
approximately the same as that in the comparative example 17. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 25 to 27 and the 
comparative examples 16 and 17 using the hydrogen absorbing alloys 
obtained in the above-mentioned manner, and nickel-hydrogen secondary 
battery were respectively fabricated using the hydrogen absorbing alloy 
electrodes as their negative electrodes. 
The internal pressure in the early stages of each of the nickel-hydrogen 
secondary batteries thus fabricated was measured in the same manner as 
described above. The results thereof were shown in the following Table 14. 
TABLE 14 
______________________________________ 
internal pressure characteristics 
(min) 
AlCl.sub.3 
amount of added anthraquinone 
(% by (ppm) 
weight) 
0.0 5.0 10.0 50.0 100.0 200.0 
______________________________________ 
embodiment 
1 125 140 140 140 135 95 
34 
embodiment 
3 125 140 145 145 140 95 
35 
embodiment 
5 130 145 145 145 145 95 
36 
comparative 
7 125 130 130 120 120 100 
example 25 
comparative 
0 125 110 120 120 90 80 
example 26 
______________________________________ 
As apparent from the results, when the amount of anthraquinone added to the 
acid solution was in the range of 5.0 ppm to 100.0 ppm, the charging time 
period indicating the internal pressure characteristics of the battery in 
each of the embodiments 34 to 36 in which the value of A/B was not less 
than 1.20 as described above was longer than that in each of the 
comparative examples 25 and 26 in which the value of A/B was less than 
1.20. Therefore, the emission of hydrogen gas in the early stages was 
restrained, so that a sufficient discharge capacity was obtained from the 
early stages. (Embodiments 37 to 39 and Comparative Example 27) 
In the embodiments 37 to 39 and the comparative example 27, in 
surface-treating in an acid solution the above-mentioned hydrogen 
absorbing alloys, the initial pH of the acid solution was set to 1.0, and 
the liquid temperature thereof was set to 25.degree. C. as in the 
embodiments 25 to 27 and the comparative examples 16 to 18, and 50 ppm of 
anthraquinone was added, while aluminum hydroxide Al(OH).sub.3 was added 
as an aluminum compound to the acid solution in a proportion as shown in 
the following Table 15. 
The abundance ratio of each type of atoms in a portion to a depth of 30 
.ANG. from the surface of each of the hydrogen absorbing alloys 
surface-treated in the above-mentioned manner was measured in the 
above-mentioned manner. 
The sum A of the respective abundance ratios of Co atoms, Al atoms and Mn 
atoms in the portion to a depth of 30 .ANG. from the surface of each of 
the hydrogen absorbing alloys was found, and the sum B of the respective 
abundance ratios of Co atoms, Al atoms and Mn atoms in a bulk region 
inside the hydrogen absorbing alloy was found, to calculate A/B in the 
same manner as described above. The results thereof were together shown in 
the following Table 15. 
TABLE 15 
______________________________________ 
embodi- 
embodi- 
ment ment embodiment 
comparative 
37 38 39 example 27 
______________________________________ 
treating conditions 
of acid solution 
pH 1.0 1.0 1.0 1.0 
liquid temperature 
25 25 25 25 
(.degree. C.) 
anthraquinone (ppm) 
50 50 50 50 
Al(OH).sub.3 (% by weight) 
1 3 5 7 
abundance ratio of 
atoms on surface 
Co (atm/%) 20.10 21.02 23.09 20.09 
Al (atm/%) 2.43 2.66 3.01 2.34 
Mn (atm/%) 4.88 5.32 6.01 3.76 
A (atm/%) 27.41 29.00 32.11 26.19 
abundance ratio of 
atoms inside 
B (atm/%) 22.30 22.90 23.46 22.09 
A/B 1.23 1.27 1.37 1.19 
______________________________________ 
As a result, in the hydrogen absorbing alloys in the embodiments 37 to 39, 
the value of A/B was not less than 1.20, which satisfied the conditions of 
the present invention. On the other hand, in the hydrogen absorbing alloy 
in the comparative example 27 which was treated using an acid solution to 
which 7% by weight, which is more than 5% by weight, of Al(OH).sub.3 was 
added, the value of A/B was less than 1.20. 
(Embodiments 40 to 42 and Comparative Example 28) 
In the embodiments 40 to 42 and the comparative example 28, in 
surface-treating in an acid solution the above-mentioned hydrogen 
absorbing alloys, the liquid temperature of the acid solution was set to 
25.degree. C., and 50 ppm of anthraquinone was added to the acid solution 
as in the embodiments 37 to 39 and the comparative example 27, and the 
amount of aluminum hydroxide Al(OH).sub.3 added to the acid solution in 
the embodiment 40 was made the same as that in the embodiment 37, the 
amount in the embodiment 41 was made the same as that in the embodiment 
38, the amount in the embodiment 42 was made the same as that in the 
embodiment 39, and the amount in the comparative example 28 was made the 
same as that in the comparative example 27 as shown in the following Table 
16, while the initial pH of the acid solution was changed as shown in the 
same table, to respectively surface-treat the hydrogen absorbing alloys. 
Even when the initial pH of the acid solution was changed as described 
above, the value of A/B was hardly changed, that is, the value in the 
embodiment 40 was approximately the same as that in the embodiment 37, the 
value in the embodiment 41 was approximately the same as that in the 
embodiment 38, the value in the embodiment 42 was approximately the same 
as that in the embodiment 39, and the value in the comparative example 28 
was approximately the same as that in the comparative example 27. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 25 to 27 and the 
comparative examples 16 and 17 using the hydrogen absorbing alloys 
obtained in the above-mentioned manner. 
The internal pressure in the early stages of each of the nickel-hydrogen 
secondary batteries thus fabricated was measured in the same manner as 
described above. The results thereof were shown in the following Table 16. 
TABLE 16 
______________________________________ 
internal pressure characteristics 
Al(OH).sub.3 (min) 
(% by pH 
weight) 0.5 0.7 1.0 1.5 2.0 3.0 
______________________________________ 
embodiment 
1 95 135 135 140 135 95 
40 
embodiment 
3 100 140 140 140 140 100 
41 
embodiment 
5 100 145 145 145 135 95 
42 
comparative 
7 95 120 125 125 110 90 
example 28 
______________________________________ 
As apparent from the results, when the initial pH of the acid solution was 
changed, the charging time period indicating the internal pressure 
characteristics of the battery in each of the embodiments 40 to 42 in 
which the value of A/B was not less than 1.20 was longer than that in the 
comparative example 28 in which the value of A/B was less than 1.20. 
Therefore, the emission of hydrogen gas in the early stages was 
restrained, so that a sufficient discharge capacity was obtained from the 
early stages. 
In surface-treating the hydrogen absorbing alloy in the acid solution as 
described above, when the hydrogen absorbing alloy was treated in the acid 
solution whose initial pH was in the range of 0.7 to 2.0, the internal 
pressure characteristics of each of the nickel-hydrogen secondary 
batteries were further improved. 
(Embodiments 43 to 45 and Comparative Example 29) 
In the embodiments 43 to 45 and the comparative example 29, in 
surface-treating in an acid solution hydrogen absorbing alloys, the 
initial pH of the acid solution was set to 1.0, and 50 ppm of 
anthraquinone was added to the acid solution as in the embodiments 37 to 
39 and the comparative example 27, and the amount of Al(OH).sub.3 added to 
the acid solution in the embodiment 43 was made the same as that in the 
embodiment 37, the amount in the embodiment 44 was made the same as that 
in the embodiment 28, the amount in the embodiment 45 was made the same as 
that in the embodiment 29, and the amount in the comparative example 29 
was made the same as that in the comparative example 27 as shown in the 
following Table 17, while the liquid temperature of the acid solution was 
changed as shown in the same table, to respectively surface-treat the 
hydrogen absorbing alloys. 
Even when the liquid temperature of the acid solution was changed as 
described above, the value of A/B was hardly changed, that is, the value 
in the embodiment 43 was approximately the same as that in the embodiment 
37, the value in the embodiment 44 was approximately the same as that in 
the embodiment 38, the value in the embodiment 45 was approximately the 
same as that in the embodiment 39, and the value in the comparative 
example 29 was approximately the same as that in the comparative example 
27. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 25 to 27 and the 
comparative examples 16 and 17 using the hydrogen absorbing alloys 
obtained in the above-mentioned manner. 
The internal pressure in the early stages of each of the nickel-hydrogen 
secondary batteries thus fabricated was measured in the same manner as 
described above. The results thereof were shown in the following Table 17. 
TABLE 17 
______________________________________ 
internal pressure characteristics 
(min) 
Al(OH).sub.3 liquid temperature of acid solution 
(% by (.degree. C.) 
weight) 10.0 25.0 40.0 60.0 70.0 80.0 
______________________________________ 
embodiment 
1 120 135 145 145 140 95 
43 
embodiment 
3 120 140 145 145 140 95 
44 
embodiment 
5 120 145 145 145 145 95 
45 
comparative 
7 120 125 125 130 115 95 
example 29 
______________________________________ 
As apparent from the results, when the liquid temperature of the acid 
solution was set in the range of 25.0.degree. C. to 70.0.degree. C., the 
charging time period indicating the internal pressure characteristics of 
the battery in each of the embodiments 43 to 45 in which the value of A/B 
was not less than 1.20 as described above was longer than that in the 
comparative example 29 in which the value of A/B was less than 1.20. 
Therefore, the emission of hydrogen gas in the early stages was 
restrained, so that a sufficient discharge capacity was obtained from the 
early stages. 
(Embodiments 46 to 48 and Comparative Example 30) 
In the embodiments 46 to 48 and the comparative example 30, in 
surface-treating in an acid solution hydrogen absorbing alloys, the 
initial pH of the acid solution was set to 1.0, the liquid temperature 
thereof was set to 25.degree. C. as in the embodiments 37 to 39 and the 
comparative example 27, and the amount of aluminum hydroxide Al(OH).sub.3 
added to the acid solution in the embodiment 46 was made the same as that 
in the embodiment 37, the amount in the embodiment 47 was made the same as 
that in the embodiment 38, the amount in the embodiment 49 was made the 
same as that in the embodiment 39, and the amount in the comparative 
example 30 was made the same as that in the comparative example 27 as 
shown in the following Table 18, while the amount of anthraquinone added 
to the acid solution was changed as shown in the same table, to 
respectively surface-treat the hydrogen absorbing alloys. 
Even when the amount of anthraquinone added to the acid solution was 
changed as described above, the value of A/B was hardly changed, that is, 
the value in the embodiment 46 was approximately the same as that in the 
embodiment 37, the value in the embodiment 47 was approximately the same 
as that in the embodiment 38, the value in the embodiment 48 was 
approximately the same as that in the embodiment 39, and the value in the 
comparative example 30 was approximately the same as that in the 
comparative example 27. 
Hydrogen absorbing alloy electrodes were then respectively fabricated in 
the same manner as described in the embodiments 25 to 27 and the 
comparative examples 16 and 17 using the hydrogen absorbing alloys 
obtained in the above-mentioned manner. 
The internal pressure in the early stages of each of the nickel-hydrogen 
secondary batteries thus fabricated was measured in the same manner as 
described above. The results thereof were shown in the following Table 18. 
TABLE 18 
______________________________________ 
internal pressure characteristics 
(min) 
Al(OH).sub.3 amount of added anthraquinone 
(% by (ppm) 
weight) 0 5 10 50 100 200 
______________________________________ 
embodiment 
1 125 140 140 135 135 95 
46 
embodiment 
3 125 145 145 140 140 95 
47 
embodiment 
48 5 130 145 145 145 145 95 
comparative 
7 125 130 130 125 125 95 
example 30 
______________________________________ 
As apparent from the results, when the amount of anthraquinone added to the 
acid solution was in the range of 5 ppm to 100 ppm, the charging time 
period indicating the internal pressure characteristics of the battery in 
each of the embodiments 46 to 48 in which the value of A/B was not less 
than 1.20 as described above was longer than that in the comparative 
example 30 in which the value of A/B was less than 1.20. Therefore, the 
emission of hydrogen gas in the early stages was restrained, so that a 
sufficient discharge capacity was obtained from the early stages. 
Although the present invention has been fully described by way of examples, 
it is to be noted that various changes and modification will be apparent 
to those skilled in the art. 
Therefore, unless otherwise such changes and modifications depart from the 
scope of the present invention, they should be construed as being included 
therein.