Alkaline storage battery and method for charging battery

In an alkali storage battery comprising a positive electrode, a negative electrode and an alkali electrolyte in a battery can, .alpha.-nickel hydroxide containing manganese is used as a cathode active material for the positive electrode, and the difference between a charging potential and an oxygen gas evolution potential at the positive electrode is increased, to suppress oxygen gas evolution during the charging, and the volume percentage of the cathode active material and an anode active material is set to not less than 75% in the battery can, to obtain a large battery capacity.

TECHNICAL FIELD 
The present invention relates to an alkali storage battery such as a 
nickel-zinc storage battery, a nickel-cadmium storage battery, or a 
nickel-metal hydride storage battery using nickel hydroxide for its 
positive electrode and a method of charging, and more particularly, to an 
alkali storage battery, whose energy density can be increased by 
suppressing oxygen gas evolution during the charging and a method of 
charging. 
BACKGROUND ART 
Conventionally in an alkali storage battery such as a nickel-zinc storage 
battery, a nickel-cadmium storage battery, or a nickel-metal hydride 
storage battery, nickel hydroxide has been generally used as a cathode 
active material for its positive electrode. 
In the case of the alkali storage battery thus using nickel hydroxide as a 
cathode active material for its positive electrode, electrochemical 
reversibility is very superior. However, oxygen gas is easily generated 
from the positive electrode during the charging. Consequently, this oxygen 
gas evolution makes it difficult for batteries to charge. 
In addition, the pressure rises in the battery by oxygen gas evolution, so 
that an electrolyte solution (hereinafter referred to as an electrolyte) 
leaks from the battery, and charge/discharge cycle performance is 
degraded. 
In the above-mentioned alkali storage battery, various methods have been 
conventionally considered. For example, a void inside the battery has been 
enlarged in order to prevent the pressure in the battery from rising by 
oxygen gas evolution, and the area of its negative electrode has been 
increased in order to absorb oxygen gas at the negative electrode. 
In such a case, however, there are some problems. For example, the energy 
density of the alkali storage battery is decreased. Therefore, a battery 
capacity cannot be obtained sufficiently. 
On the other hand, when manganese dioxide electrode is used for a positive 
electrode of an alkali manganese battery, it is possible to suppress the 
oxygen gas evolution during the charging. However, the reversibility of 
manganese dioxide electrode is very poor. 
There have been conventionally various developments in order to improve 
characteristics in an alkali storage battery using nickel hydroxide as an 
active material for its positive electrode as described above. 
Proposed as the developments include one where at least one type of 
manganese, silver, cobalt and their compounds are mixed with nickel 
hydroxide to produce a large-capacity nickel electrode, as disclosed in 
JP, 54-4334, A; one containing a manganese compound in a positive 
electrode to obtain a battery which is hardly self-discharged and has a 
low life, as disclosed in JP, 5-121073, A; one containing at least one 
type of cadmium, calcium, zinc, magnesium, iron, cobalt and manganese in 
an active material composed of powdered nickel hydroxide, to inhibit 
swelling of a positive electrode and improve the energy density and the 
cycle life, as disclosed in JP, 5-21064, A; and one where that not less 
than 50% of manganese exists in a state where its valence is 3 in nickel 
hydroxide containing manganese, to improve the active material utilization 
of nickel hydroxide, as disclosed in JP, 7-335214, A. 
Even in the developments disclosed in the above-mentioned publications, a 
method of effectively suppressing oxygen gas evolution during the charging 
is not disclosed. Therefore, the pressure in the battery still rises by 
oxygen gas evolution, so that there are some problems. For example, an 
electrolyte leaks from the battery, and charge/discharge cycle performance 
is degraded. 
An object of the present invention is to solve the above-mentioned problems 
in an alkali storage battery such as a nickel-zinc storage battery, a 
nickel-cadmium storage battery, or a nickel-metal hydride storage battery 
using nickel hydroxide as a cathode active material for its positive 
electrode. 
Specifically, an object of the present invention is to make it possible to 
simply suppress, in an alkali storage battery using nickel hydroxide as a 
cathode active material for its positive electrode, oxygen gas evolution 
during the charging of the battery. 
Another object is to obtain an alkali storage battery having a large 
battery capacity by increasing the energy density of the battery without 
enlarging a void inside the battery and increasing the area of its 
negative electrode such that oxygen gas is absorbed at the negative 
electrode, as in the conventional example, in order to inhibit the 
pressure in the battery from rising by oxygen gas evolution during the 
charging. 
Still another object is to obtain an alkali storage battery which is 
superior in charge/discharge cycle performance. 
DISCLOSURE OF INVENTION 
An alkali storage battery according to the present invention is an alkali 
storage battery comprising a positive electrode, a negative electrode and 
an alkali solution as an electrolyte in a battery can, wherein 
.alpha.-nickel hydroxide containing manganese is used as a cathode active 
material for the positive electrode, and the volume percentage of the 
cathode active material and an anode active material in a containing 
portion of the battery can is not less than 75%. 
As in the alkali storage battery according to the present invention, when 
.alpha.-nickel hydroxide containing manganese is used as the cathode 
active material for the positive electrode, the difference between an 
oxygen gas evolution potential and a charging potential at the positive 
electrode is increased, so that the alkali storage battery can be simply 
charged to a predetermined potential while suppressing oxygen gas 
evolution during the charging without decreasing the voltage and the 
battery capacity in the alkali storage battery. 
Therefore, in the alkali storage battery according to the present 
invention, the necessities of spirally winding an electrode to enlarge a 
void inside the battery and increasing the area of its negative electrode 
such that oxygen gas is absorbed at the negative electrode as in the 
conventional alkali storage battery are eliminated. 
It is possible to charge the alkali storage battery to a predetermined 
potential while suppressing oxygen gas evolution during the charging as 
described above. Even when the battery is fabricated so as to have an 
inside out structure in which the volume percentage of the cathode active 
material and the anode active material in the containing portion of the 
battery can is not less than 75%, therefore, no leakage of an electrolyte 
from the battery occurs by the rise in the pressure in the battery, and 
charge/discharge cycle performance is not degraded. Therefore, the alkali 
storage battery has a high energy density and a large battery capacity. 
In the present invention, the oxygen gas evolution potential means a 
potential at the time point where charging is performed at an 
electrochemical equivalent which is 1.5 times as large as that for the 
cathode active material, and the charging potential means a potential at 
the time point where charging is performed at an electrochemical 
equivalent which is 0.5 times as large as that for the cathode active 
material. 
In the alkali storage battery according to the present invention, if the 
amount of manganese contained in the cathode active material is less, the 
difference between the oxygen gas evolution potential and the charging 
potential at the positive electrode is decreased, so that oxygen is easily 
generated during the charging. On the other hand, if the amount of 
manganese is too large, the ratio of nickel hydroxide in the cathode 
active material is decreased, so that the battery capacity is decreased. 
Therefore, the amount of manganese in the cathode active material is 
preferably in the range of 8 to 60 mole %, and more preferably in the 
range of 15 to 40 mole %. 
By including manganese in .alpha.-nickel hydroxide as described above, the 
alkali storage battery is prevented from being self-discharged, for 
example, in such a manner that manganese is uniformly contained in 
.alpha.-nickel hydroxide, so that it is desirable to uniformly dissolve 
and precipitate manganese in .alpha.-nickel hydroxide using nickel sulfate 
or manganese sulfate. 
By thus including manganese in the cathode active material so as, to adjust 
the difference between the oxygen gas evolution potential and the charging 
potential at the positive electrode, oxygen is sufficiently suppressed 
during the charging without decreasing the voltage and the battery 
capacity in the alkali storage battery. Therefore, the charging potential 
is preferably 120 to 300 mV, more preferably 120 to 180 mV lower than the 
oxygen gas evolution potential. 
When a potential at the positive electrode at which the charging is stopped 
is 120 to 300 mV, preferably 120 to 180 mV lower than the oxygen gas 
evolution potential, oxygen gas evolution is suppressed during the 
charging, so that no electrolyte leaks from the alkali storage battery, 
and the alkali storage battery can be sufficiently charged. Further, the 
voltage and the battery capacity in the alkali storage battery are not 
decreased. 
In the alkali storage battery in the present invention, the anode active 
material used for the negative electrode is not particularly limited, 
provided that it is generally used in an alkali storage battery. However, 
it is preferable that zinc having a low redox potential is used as the 
anode active material for the negative electrode in order that sufficient 
battery voltage is obtained even when the difference between the oxygen 
gas evolution potential and the charging potential at the positive 
electrode is increased as described above.

BEST MODE FOR CARRYING OUT THE INVENTION 
An alkali storage battery according to an embodiment of the present 
invention and a method of charging will be specifically described, and it 
will be clarified by taking comparative examples, to show that in the 
alkali storage battery in the present embodiment, oxygen gas evolution is 
sufficiently suppressed during the charging, so that the battery capacity 
can be increased, and superior charge/discharge cycle performance is 
obtained. The alkali storage battery and the method of charging in the 
present invention are not particularly limited to those described in the 
following embodiments, and can be embodied by being suitably changed 
within a range in which the gist thereof is not changed. 
Embodiment 1 
In the present embodiment, a solution of nickel sulfate and a solution of 
manganese sulfate were mixed such that the molar ratio of manganese 
sulfate to nickel sulfate would be 1:9. 
10% ammonia aq. solutions water and a 10% solution of sodium hydroxide ag. 
solution were added to the mixed solution, and were adjusted such that the 
pH would be 10.0.+-.0.4 to form a precipitate. The precipitate was 
filtered, and was then preserved at room temperature in a 20% potassium 
hydroxide aq. solution for one week, after which the precipitate was 
cleaned, and was filtered, to obtain a cathode active material containing 
manganese in .alpha.-nickel hydroxide. 
In the cathode active material thus obtained, the content of manganese was 
10 mole %, and the mean particle diameter thereof was 10 .mu.m. 
The cathode active material with, graphite serving as a conductive 
material, cobalt hydroxide serving as a conductive material, and powdered 
polytetrafluoroethylene (PTFE) serving as a binder, were kneaded in a 
weight ratio of 84:8:3:5. 
Comparative Example 1 
In comparative example 1, for producing a cathode active material, cobalt 
sulfate was used in place of manganese sulfate in the above-mentioned 
embodiment 1. A positive electrode agent was obtained in the same manner 
as that in the embodiment 1 except that the molar ratio of nickel sulfate 
to cobalt sulfate would be 1:9. 
Comparative Example 2 
In comparative example 2, for producing a cathode active material, cadmium 
sulfate was used in place of manganese sulfate in the above-mentioned 
embodiment 1. A positive electrode agent was obtained in the same manner 
as that in the embodiment 1 except that the molar ratio of nickel sulfate 
to cadmium sulfate would be 1:9. 
Comparative Example 3 
In comparative example 3, for producing a cathode active material, zinc 
sulfate was used in place of manganese sulfate in the above-mentioned 
embodiment 1. A positive electrode agent was obtained in the same manner 
as that in the embodiment 1 except that the molar ratio of nickel sulfate 
to zinc sulfate would be 1:9. 
Comparative Example 4 
In comparative example 4, for producing a cathode active material, 
magnesium sulfate was used in place of manganese sulfate in the 
above-mentioned embodiment 1. A positive electrode agent was obtained in 
the same manner as that in the embodiment 1 except that the molar ratio of 
nickel sulfate to magnesium sulfate would be 1:9. 
Comparative Example 5 
In comparative example 5, for producing a cathode active material, calcium 
sulfate was used in place of manganese sulfate in the above-mentioned 
embodiment 1. A positive electrode agent was obtained in the same manner 
as that in the embodiment 1 except that the molar ratio of nickel sulfate 
to calcium sulfate would be 1:9. 
Comparative Example 6 
In comparative example 6, for producing a cathode active material, aluminum 
sulfate was used in place of manganese sulfate in the above-mentioned 
embodiment 1. A positive electrode agent was obtained in the same manner 
as that in the embodiment 1 except that the molar ratio of nickel sulfate 
to aluminum sulfate would be 1:9. 
With respect to each of the cathode active materials obtained in embodiment 
1 and in comparative examples 1 to 6, the crystal structure was analyzed 
by an X-ray diffraction method (XRD). From the results, the cathode active 
materials in embodiment 1 and in comparative example 1 had an a-nickel 
hydroxide structure, while the cathode active materials in the comparative 
examples 2 to 6 had a B-nickel hydroxide structure. 
1 g of each of the positive electrode agents in the embodiment 1 and the of 
comparative examples 1 to 6 was formed by pressure into the shape of a 
disk having a diameter of 20 mm, after which a collector was mounted 
thereon, to fabricate a positive electrode for testing. 
A sintering-type cadmium electrode having an excessive capacity as a 
negative electrode, as compared with the capacity of each of the 
above-mentioned positive electrodes for testing, was used, so as to 
fabricate a battery for testing which used an excessive alkali solution 
for electrolyte. A cadmium electrode charged up to 50% of the capacity was 
used as a reference electrode. 
In measuring an oxygen gas evolution potential V1 and a charging potential 
V2 at each of the positive electrodes for testing, the testing battery was 
charged at 30 mA/g for 15 hours. After the charging, it was kept for one 
hour. Thereafter, the testing battery was then discharged with constant 
current of 100 mA up to 1.0 V to measure the oxygen gas evolution 
potential V1 and the charging potential V2 at the positive electrode for 
testing as well as to find the difference (V1-V2) between the oxygen gas 
evolution potential and the charging potential, and to further find the 
number of exchanged electrons related to reaction on the basis of one mole 
of the nickel atom in the cathode active material. The results are shown 
in the following Table 1. 
TABLE 1 
______________________________________ 
number of 
oxygen gas exchanged 
positive evolution charging electrons 
electrode potential potential V1-V2 based on Ni 
agent V1 (V) V2 (V) (V) atom 
______________________________________ 
embodiment 1 
1.495 1.237 0.258 1.00 
comparative 
1.416 1.296 0.120 0.96 
example 1 
comparative 
1.428 1.305 0.123 0.93 
example 2 
comparative 
1.420 1.316 0.104 0.93 
example 3 
comparative 
1.408 1.346 0.062 0.95 
example 4 
comparative 
1.421 1.338 0.082 0.96 
example 5 
comparative 
1.395 1.368 0.027 0.85 
example 6 
______________________________________ 
As a result, in the battery tested using the positive electrode agent of 
embodiment 1, the difference between the oxygen gas evolution potential 
and the charging potential was as large as 0.258 V. On the other hand, in 
each of the batteries tested using the positive electrode agents of 
comparative examples 1 to 6, the difference between the oxygen gas 
evolution potential and the charging potential was smaller than that in 
the embodiment 1. 
The battery for testing using each of the positive electrode agents in the 
embodiment 1 and the comparative example 1 was charged and discharged as 
described above in 10 cycles, and the relationship between a potential and 
a charging capacity in the battery in the 10-th cycle was examined. The 
results were shown in FIG. 1. 
As a result, in the battery tested using the positive electrode agent in 
the embodiment 1, the rise in the voltage in a portion from the charging 
capacity of 200 mAh/g to the charging capacity of 250 mAh/g was more 
rapid, as compared with that in the battery tested using the positive 
electrode agent in the comparative example 1. 
Therefore, in the case of the battery for tested using the positive 
electrode agent in the embodiment 1, the charging voltage was set such 
that the charging capacity would be in the range of 200 to 250 mAh/g, so 
that a large battery capacity was obtained by sufficiently charging the 
battery while suppressing oxygen gas evolution during the charging. 
On the other hand, in the case of the battery tested using the positive 
electrode agent in the comparative example 1, the voltage gradually 
increased during the charging, so that it was difficult to obtain a large 
battery capacity while suppressing oxygen gas evolution during the 
charging. 
Then, the positive electrode agent in each of the embodiment 1 and the 
comparative examples 1 to 6 was used for the positive electrode. A kneaded 
mixture of zinc oxide having an average particle diameter of 0.4 .mu.m, 
zinc having an average particle diameter of 120 .mu.m, indium hydroxide 
for suppressing oxygen gas evolution, and polytetrafluoroethylene serving 
as a binder in a weight ratio of 60:35:3:2 was used as the negative 
electrode agent at the negative The positive and negative electrodes were 
fabricated into an alkali storage battery having an inside out structure 
as shown in FIG. 2. 
In fabricating each of the alkali storage batteries using the agents of 
embodiment 1 and comparative examples 1 to 6, the above-mentioned positive 
electrode agent 1a was formed in a cylindrical shape and was inserted into 
a positive electrode can 1b, to construct a positive electrode 1. An 
alkali solution as an electrolyte was impregnated in a separator 3 
obtained by laminating cellophane and a polyolefin nonwoven fabric, and 
the separator 3 was provided around a hollow portion at the center of the 
positive electrode 1. The hollow portion of the positive electrode 1 was 
filled with the above-mentioned negative electrode agent 2a through the 
separator 3, and a negative electrode collector 2b in the shape of a stick 
was arranged at its central part to construct a negative electrode 2, 
thereby fabricating an alkali storage battery having an inside out 
structure. 
Each of the alkali storage batteries according to embodiment 1 and 
comparative examples 1 to 6 fabricated in the above-mentioned manner was 
then charged with constant current of 100 mA up to 1.95 V, was preserved 
at a temperature of 40.degree. C. for one week, and was then discharged 
with constant current of 100 mA up to 1.0 V to measure a charging capacity 
C1 and a discharging capacity C2 as well as to find the ratio of the 
discharging capacity C2 to the charging capacity C1 (C2/C1). Further, 10 
alkali storage batteries according to each of embodiment 1 and comparative 
examples 1 to 6 were charged and discharged, as described above, to find 
the number of alkali storage batteries from which electrolyte leaks. The 
results were shown in the following Table 2. 
TABLE 2 
______________________________________ 
number of 
charging discharging batteries from 
capacity C1 
capacity C2 which alkali 
battery (mAh) (mAh) C2/C1 solution leaks 
______________________________________ 
embodiment 1 
1680 1630 0.97 0 
comparative 
1570 1380 0.87 3 
example 1 
comparative 
1580 1410 0.89 2 
example 2 
comparative 
1480 1270 0.85 5 
example 3 
comparative 
1360 890 0.65 9 
example 4 
comparative 
1460 980 0.67 4 
example 5 
comparative 
1300 570 0.47 10 
example 6 
______________________________________ 
As a result, in the alkali storage battery of embodiment 1 using the 
cathode active material containing manganese in .alpha.-nickel hydroxide, 
the ratio of the discharging capacity C2 to the charging capacity Cl 
(C2/C1) was higher as compared with that in each of the alkali storage 
batteries of comparative examples 1 to 6, and leakage of the electrolyte 
such as occurred and in each of the alkali storage batteries in the 
comparative examples 1 to 6 did not occur. The reason for this was 
conceivably that when the cathode active material containing manganese in 
.alpha.-nickel hydroxide as in the alkali storage battery of embodiment 1 
was used, the difference between the charging potential and the oxygen gas 
evolution potential was increased, as shown in the foregoing Table 1, so 
that oxygen gas evolution was suppressed during the charging, nickel 
hydroxide was prevented from being unstable by being excessively oxidized, 
and the stability of the positive electrode in a charged state was 
improved. 
Experimental Example 1 
In the experimental example, the alkali storage battery in the 
above-mentioned embodiment 1 was used, and was charged and discharged in 
the same manner as that in the above-mentioned case except that the 
charging final voltage was changed as shown in the following Table 3 in 
charging the battery with constant current of 100 mA. In so doing, the 
charging capacity C1 and discharging capacity C2 were measured to find the 
ratio of the discharging capacity to the charging capacity C1 (C2/C1). 
Further, 10 alkali storage batteries were charged and discharged, as 
described above, to find the number of batteries from which electrolyte 
leaks. The results were shown in Table 3. 
TABLE 3 
______________________________________ 
charging number of 
final charging discharging batteries from 
voltage capacity C1 
capacity C2 which alkali 
(V) (mAh) (mAh) C2/C1 solution leaks 
______________________________________ 
2.13 1730 1620 0.93 3 
2.07 1710 1630 0.95 0 
2.01 1690 1640 0.97 0 
1.95 1680 1630 0.97 0 
1.83 1550 1530 0.99 0 
1.80 1420 1410 0.99 0 
______________________________________ 
As a result, when the charging final voltage was set to 2.13 V, the 
charging and discharging efficiency was reduced, and an electrolyte 
partially leaked. The reason for this was conceivably that when the 
charging final voltage was set to 2.13 V, the charging potential reached 
an oxygen gas evolution potential, so that oxygen was generated at the 
positive electrode. 
When the charging final voltage was set to 2.07 V, no electrolyte leaked, 
while the charging and discharging efficiency was slightly reduced. The 
reason for this was conceivably that nickel hydroxide at the positive 
electrode became unstable upon being excessively oxidized because the 
alkali storage battery was charged to a high potential, and was easily 
decomposed at the time of preservation. 
On the other hand, when the charging final voltage was set to not more than 
2.01 V, no electrolyte leaked, and the charging and discharging efficiency 
was increased. However, the battery capacity was decreased as the charging 
final voltage was decreased. 
In order to increase the charging and discharging efficiency while 
preventing an electrolyte from leaking as well as to make the decrease in 
the battery capacity slight, therefore, it was preferable to make the 
charging final voltage 120 to 300 mV lower than 2.13 V which is an oxygen 
gas evolution potential. In order to make the decrease in the battery 
capacity slighter, it was preferable to make the charging final voltage 
120 to 180 mV lower than the oxygen gas evolution potential. 
Experimental Example 2 
In the experimental example, in obtaining a cathode active material, nickel 
sulfate and manganese sulfate were used, as in the above-mentioned 
embodiment 1. The mixture ratio of nickel sulfate to manganese sulfate was 
changed to obtain cathode active materials composed of .alpha.-nickel 
hydroxide containing manganese whose amount was 7 mole %, 8 mole %, 10 
mole %, 15 mole %, 25 mole %, 40 mole %, 60 mole %, and 70 mole %. 
Positive electrode agents were respectively prepared in the same manner as 
that in the above-mentioned embodiment 1 using the above-mentioned cathode 
active materials. Batteries for testing were respectively fabricated in 
the same manner as that in the above-mentioned case using the positive 
electrode agents thus prepared, to measure the above-mentioned oxygen gas 
evolution potential V1 and charging potential V2 for each of the positive 
electrodes to, find the difference (V1-V2) between the oxygen gas 
evolution potential and the charging potential, and further to find the 
number of exchanged electrons related to reaction on the basis of one mole 
of the nickel atom in the cathode active material and to find the number 
of exchanged electrons related to reaction on the basis of one mole of the 
sum of the nickel atom and the manganese atom. The results were shown in 
the following Table 4. 
TABLE 4 
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oxygen gas 
evolution charging number of exchanged 
amount of 
potential potential electrons 
Mn V1 V2 V1-V2 based on 
based on 
(mole %) 
(V) (V) (V) Ni Ni + Mn 
______________________________________ 
7 1.436 1.278 0.158 0.95 0.88 
8 1.478 1.258 0.220 0.97 0.89 
10 1.495 1.237 0.258 1.00 0.90 
15 1.498 1.235 0.263 1.05 0.89 
25 1.498 1.233 0.265 1.06 0.79 
40 1.498 1.231 0.267 1.18 0.70 
60 1.496 1.228 0.268 1.35 0.54 
70 1.458 1.226 0.232 1.25 0.38 
______________________________________ 
Alkali storage batteries having an inside out structure as shown in FIG. 2 
were respectively fabricated in the same manner as that in the 
above-mentioned embodiment 1 using the above-mentioned cathode active 
materials containing manganese of varying amounts. 
Each of the alkali storage batteries thus fabricated was charged with 
constant current of 100 mA up to 1.95 V, was preserved at a temperature of 
40.degree. C. for one week, and was then discharged with constant current 
of 100 mA up to 1.0 V, after which the discharging was stopped for one 
hour. The above-mentioned charging and discharging were considered as one 
cycle. 20 cycles of charging and discharging were performed, to find a 
discharging capacity Q1 at the first cycle time and a discharging capacity 
Q20 at the 20-th cycle time as well as to calculate the percentage of 
capacity retention at the 20-th cycle time on the basis of the following 
equation. The results were shown in the following Table 5. 
Percentage of capacity retention (%)=(Q20/Q1).times.100 
TABLE 5 
______________________________________ 
percentage of 
capacity 
retention at 
discharging capacity (mAh) 
20-th cycle 
amount of Mn 
first cycle 
20-th cycle 
time 
(mole %) time time (%) 
______________________________________ 
7 1600 980 61 
8 1630 1380 85 
10 1640 1460 89 
15 1620 1550 96 
25 1580 1510 96 
40 1480 1450 98 
60 1240 1200 97 
70 980 950 97 
______________________________________ 
As apparent from the results shown in the foregoing Table 4 and Table 5, 
when the amount of manganese in the cathode active material was as low as 
7 mole %, the difference between the oxygen gas evolution potential and 
the charging potential was decreased, so that oxygen was easily generated 
during the charging, and the percentage of capacity retention at the 20-th 
cycle time was decreased, resulting in degraded charge/discharge cycle 
performance. On the other hand, when the amount of manganese in the 
cathode active material was as large as 70 mole %, the battery capacity 
was decreased. 
In order to suppress oxygen gas evolution during the charging, improve the 
charge/discharge cycle performance, and further obtain a large battery 
capacity in the above-mentioned alkali storage battery, therefore, it was 
desirable that the amount of manganese in the cathode active material was 
preferably in the range of 8 to 60 mole %, and more preferably in the 
range of 15 to 60 mole %. 
In then charging the alkali storage battery in which the amount of 
manganese in the cathode active material was 10 mole %, 20 cycles of 
charging and discharging were performed in the same manner as that in the 
above-mentioned case except that a charging current was first increased 
such that the battery was charged at a predetermined voltage of 1.90 V and 
was gradually decreased, to find a discharging capacity Q1 at the first 
cycle time and a discharging capacity Q20 at the 20-th cycle time as well 
as to calculate the percentage of capacity retention at the 20-th cycle 
time. The results, together with the results in the case where the alkali 
storage battery was charged at a predetermined charging current of 100 mA 
as described above, were shown in the following Table 6. 
TABLE 6 
______________________________________ 
percentage of 
discharging capacity 
capacity 
amount of (mAh) retention at 
Mn charging first cycle 
20-th cycle 
20-th cycle 
(mole %) 
method time time time (%) 
______________________________________ 
10 charging at 
1350 1120 83 
predetermined 
voltage 
10 charging at 
1640 1460 89 
predetermined 
current 
______________________________________ 
As a result, when the alkali storage battery was charged at a predetermined 
voltage of 1.90 V, the percentage of capacity retention at the 20-th cycle 
time was lower, as compared with that in the case where the alkali storage 
battery was charged at a predetermined charging current of 100 mA, 
resulting in degraded charge/discharge cycle performance. However, it took 
15 to 16 hours to charge the battery to 1.90 V at a predetermined charging 
current of 100 mA, while the battery could be charged in a short time 
period, i.e., two hours, when it was charged at a predetermined voltage of 
1.90 V as described above. 
INDUSTRIAL APPLICABILITY 
As described in detail above, in an alkali storage battery according to the 
present invention and a method of charging, .alpha.-nickel hydroxide 
containing manganese is used as a cathode active material for a positive 
electrode of the alkali storage battery. Therefore, the difference between 
an oxygen gas evolution potential and a charging potential at the positive 
electrode is increased, the alkali storage battery is simply charged to a 
predetermined voltage while suppressing oxygen gas evolution without 
decreasing a voltage in the alkali storage battery, and the range of a 
voltage at which charging and discharging can be performed is widened, so 
that a large battery capacity is obtained, and charge/discharge cycle 
performance is also improved. 
In the alkali storage battery according to the present invention and a 
method of charging, the battery can be simply charged to a predetermined 
potential while suppressing oxygen gas evolution as described above. As a 
result, it is possible to fabricate a battery having an inside out 
structure to increase the energy density of the battery without enlarging 
a void inside the battery and increasing the area of its negative 
electrode such that oxygen gas is absorbed at the negative electrode as in 
the conventional example.