Sealed alkaline storage battery and method of producing negative electrode thereof

Disclosed is an alkaline storage battery using a negative electrode formed of a hydrogen absorbing alloy capable of absorbing/desorbing hydrogen electrochemically. A three-dimensional structural matter having hydrophobic property is used as a supporter for supporting the hydrogen absorbing alloy of the negative electrode, so that hydrophobic property is given to the surface of the hydrogen absorbing alloy which is in contact with the support, whereby a hydrogen gas generated in a charging period is absorbed by powder of the alloy exposed at a gas phase portion to suppress the increase of the internal gas pressure of the battery. According to the present invention, it is possible to perform rapid charge in a short time because the increase of the internal gas pressure of the battery can be suppressed.

BACKGROUND OF THE INVENTION 
The present invention relates to a sealed alkaline storage battery using a 
negative electrode of a hydrogen absorbing alloy capable of 
electrochemically absorbing/desorbing hydrogen acting as an active 
material. 
Recently, hydrogen absorbing alloys capable of electro-chemically 
absorbing/desorbing hydrogen acting as an active material have attracted 
attention for use as a negative electrode material having high energy 
density. High-capacity sealed storage batteries such as a sealed 
nickel-hydrogen storage battery and a closed manganese dioxide-hydrogen 
storage battery have been developed by combining this type negative 
electrodes and available positive electrodes such as a nickel positive 
electrode and a manganese dioxide positive electrode. In the past, this 
type negative electrodes for use in the sealed nickel-hydrogen storage 
battery and methods of producing this type negative electrodes have been 
proposed as follows. 
(1) A method of producing a negative electrode comprising filling a nickel 
porous matter having a three-dimensional structure with hydrogen absorbing 
alloy powder together an alkali-resisting binding agent (Japanese Patent 
Unexamined Publication No. 53-38631). 
(2) A method of producing a negative electrode comprising the steps of: 
applying hydrogen absorbing alloy powder to a supporting metal; and 
sintering the alloy powder in an atmosphere of an inert gas (Japanese 
Patent Unexamined Publication No. 62-278754). 
(3) A method of producing a negative electrode comprising the steps of: 
kneading hydrogen absorbing alloy powder and polytetrafluoroethylene 
(hereinafter referred to as "PTFE") powder or its aqueous solution 
dispersion while applying shearing stress thereto; pressing the kneaded 
matter to prepare a sheet; and sticking the sheet to a nickel net or the 
like (Japanese Patent Unexamined Publication No. 60-136162). 
(4) A method in which at least one portion of a negative electrode formed 
of a hydrogen absorbing alloy is provided with a hydrophobic layer 
(Japanese Patent Unexamined Publication No. 61-118963). 
The negative electrodes produced by the aforementioned methods have a 
disadvantage in that short-time (about an hour) charging required in 
various types of portable apparatus and the like is difficult or in that 
the reliability of the battery may deteriorate with repetition of 
charging/discharging though short-time (rapid) charging may be made in the 
early stage where the battery is just constructed. When the prior art 
negative electrodes formed by the above methods (1) and (2) are subject to 
relatively slow charging with respect to which the time required for 
perfect charging is within a range of from about 4.5 hours to about 16 
hours, there arises no problem particularly awaiting solution. When the 
prior art negative electrodes produced by the above methods (1) and (2) 
are subject to rapid charging, however, the internal gas pressure of the 
battery increases in an overcharging period so that a safety vent (which 
is, in general, actuated by the battery inner pressure of 10 to 15 
kg/cm.sup.2 in the same manner as an ordinary nickel-cadmium battery) is 
actuated so that the alkaline electrolyte of the battery leaks to 
constitute an obstacle to various battery characteristics and safety. 
Accordingly, in the prior art negative electrodes produced by the above 
methods (1) and (2), short-time charging is impossible. 
In the prior art negative electrode produced by the above method (3), the 
respective sheets composed of fiber-like fluororesin and hydrogen 
absorbing alloy powder are located on the opposite sides of the nickel net 
respectively. In the configuration of the negative electrode, the 
fiber-like fluororesin gives suitable hydrophobic property to the surfaces 
of the hydrogen absorbing alloy powders to improve gas absorption ability 
in an overcharging period to thereby make it possible to perform 
short-time charging in the early stage where the battery is just 
constructed. It is however very difficult to prepare reproducibly similar 
sheets by the aforementioned steps of; kneading hydrogen absorbing alloy 
powder and PTFE powder while applying shearing stress thereto; and 
pressing the mulled matter. Accordingly, the internal gas pressure of the 
battery in a short-time charging period varies widely and sometimes 
exceeds 20 kg/cm.sup.2. Furthermore, the negative electrode is inferior in 
mechanical strength because the sheet formed by tangling the alloy 
particles with the fluororesin fibers is stuck to the nickel net. 
Accordingly, the alloy and the fluororesin are subject to 
expansion/contraction due to repetition of charging/discharging and 
changes in temperature, resulting in deterioration in the negative 
electrode. Accordingly, the prior art negative electrode produced by the 
above method (3) has a problem in that the reliability of the battery 
deteriorates with repetition of charging/discharging. 
The proposal by the above method (4) is that a hydrophobic layer is 
provided in a portion of a negative electrode to thereby improve gas 
absorption capacity in an overcharging period. Although short-time 
charging is possible in this case, there arises a problem in that the 
hydrophobic layer provided in the negative electrode is made to come off 
by the expansion/contraction of the alloy due to repetition of 
charge/discharge or by a gas generated, so that the internal gas pressure 
of the battery increases with repetition of charging/discharging cycles. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to solve the 
aforementioned problems in the prior art. 
That is to say the object of the invention is to provide a highly reliable 
sealed alkaline storage battery in which the battery internal gas pressure 
never rises over the actuation pressure of a safety vent even if 
short-time charging is performed, and never rises even if 
charging/discharging cycles are repeated. 
In order to achieve the above objects, according to the present invention, 
in a sealed alkaline storage battery comprising a positive electrode 
constituted mainly by a metal oxide, a negative electrode constituted 
mainly by a hydrogen absorbing alloy capable of absorbing/ desorbing 
hydrogen acting as an active material and a support for supporting said 
alloy, an alkaline electrolyte, and a separator, the supporter is made to 
have a three-dimensional structure having hydrophobic property. Further, 
in the above-mentioned sealed alkaline storage battery, the supporter is 
made to have a three-dimensional structure having hydrophobic property and 
a surface portion of the negative electrode is provided with hydrophobic 
property. 
Further, according to the present invention, the method of producing a 
negative electrode for the above-mentioned sealed alkaline storage battery 
comprises the steps of: depositing a fluororesin on a skeletal portion of 
a nickel porous matter having a three-dimensional structure; fixing the 
fluororesin to the skeletal portion of the nickel porous matter by heat 
treatment at a temperature lower than the temperature of decomposition of 
the fluororesin to thereby prepare a support having a hydrophobic portion, 
and preparing a negative electrode through filling the support with paste 
mainly containing a hydrogen absorbing alloy, drying the electrode and 
then pressing/cutting the electrode into predetermined thickness and size.

DETAILED DESCRIPTION OF THE INVENTION 
The principle of sealed cell construction in a nickel-hydrogen storage 
battery is the same as that in a nickel-cadmium battery which has been 
proposed by Neumann. Also in the nickel-hydrogen storage battery, the 
maximum charge capacity of the negative electrode is established to be 
larger than the maximum charge capacity of the positive electrode. That is 
to say, the negative electrode is not perfectly charged even in the 
condition that the positive electrode has been perfectly charged. 
Accordingly, hydrogen gas is prevented from being generated from the 
negative electrode in an overcharging period. At the same time, oxygen gas 
generated from the positive electrode is reduced on the negative electrode 
by the reaction represented by the following formula (1) to keep the 
closing state of the battery. 
EQU MH.sub.x +O.sub.2 .fwdarw.MH.sub.x-4 +2H.sub.2 O (1) 
In the formula (1) M represents a hydrogen absorbing alloy. 
However, in the case where the negative electrode using a hydrogen 
absorbing alloy is charged, the hydrogen absorbing reaction and the 
hydrogen generation reaction respectively represented by the following 
formula (2) and (3) occur in the last stage of the charging period. The 
reaction of the formula (3) occurs more easily as the battery is charged 
more rapidly. 
##STR1## 
In the formula (2) M represents a hydrogen absorbing alloy. 
EQU H.sub.2 O+e.sup.- .fwdarw.OH.sup.- +H.sub.2 .uparw. (3) 
Accordingly, the increase of the internal gas pressure of the sealed 
nickel-hydrogen storage battery in the overcharging period is caused by 
both oxygen gas generated from the positive electrode and hydrogen gas 
generated from the negative electrode. In this battery system, the 
reaction of oxygen gas reduction represented by the formula (1) progresses 
relatively rapidly even in the case where the battery is subject to rapid 
charging. Accordingly, the increase of the battery internal pressure 
caused by oxygen gas is not important in this battery system. On the other 
hand, in the case where the negative electrode is prepared by an ordinary 
producing method, hydrogen gas generated in accordance with the formula 
(3) is difficult to absorb. Accordingly, the increase of the battery 
internal pressure caused by hydrogen gas becomes severer as the battery is 
charged more rapidly. 
According to the present invention, a supporter of a three-dimensional 
structure having hydrophobic property is used in the negative electrode, 
so that when the negative electrod is assembled, a hydrophobic property is 
given to the surfaces of hydrogen absorbing alloy particles which are in 
contact with the supporter. Accordingly, hydrogen gas generated by the 
reaction represented by the formula (3) is absorbed smoothly into the 
alloy powders being not in contact with the electrolytic solution, by the 
gas phase reaction represented by the following formula (4) to thereby 
suppress increase of the battery internal gas pressure, because the 
hydrogen absorbing alloy of the negative electrode has a sufficient 
absorption capacity. 
EQU M+H.sub.2 .fwdarw.MH.sub.2 (4) 
In the formula (2) M represents a hydrogen absorbing alloy. 
If a portion having a hydrophobic layer is further provided on the surface 
portion of the negative electrode, the reaction of the formula (4) 
progresses so much more rapidly that the battery inner pressure is little 
increased in a rapid charging period. 
According to the aforementioned construction of the negative electrode, the 
hydrogen absorbing alloy particles are kept in the three-dimensional 
porous matter having hydrophobic property to improve the mechanical 
strength thereof to thereby prevent lowering of hydrophobic property 
caused by repetition of charging/discharging. Further, the negative 
electrode is not affected by expansion/contraction of the hydrogen 
absorbing alloy, so that the internal gas pressure of the battery is 
increased little regardless of repetition of charging/discharging cycles. 
Also in the case where the nickel porous matter having a three-dimensional 
structure is filled with paste mainly containing hydrogen absorbing alloy 
powder in accordance with the negative electrode producing method of the 
present invention, the fluororesin is not easily disconnected from the 
nickel porous matter because the fluororesin is fixed to the skeletal 
portion of the nickel porous matter. Accordingly, sufficient hydrophobic 
property can be given to the surfaces of the hydrogen absorbing alloy 
particles. Further, because the fluororesin is fixed to the nickel porous 
matter having a three-dimensional structure, the fluororesin is not easily 
disconnected from the skeleton of the nickel porous matter regardless of 
expansion of the negative electrode caused by repetition of 
charging/discharging, so that stable internal gas pressure of the battery 
can be obtained. 
EMBODIMENTS 
EXAMPLE 1 
Now, the present invention will be described in conjunction with various 
examples. FIGS. 1A and 1B show a supporter of a three-dimensional 
structure having hydrophobic property as an embodiment of the present 
invention. FIG. 1A is a sectional view of the supporter, and FIG. 1B is a 
typical enlarged view of the supporter. In FIGS. 1A and 1B, the reference 
numeral 1 designates a fluoreresin, 2 a skeleton formed of nickel, and 3 a 
supporter having a three-dimensional structure. The supporter of a 
three-dimensional structure having hydrophobic property was prepared as 
follows. An available sponge-like nickel porous matter (30 mg/cm.sup.2 by 
weight per apparent unit area) having a porosity of 95% was dipped into an 
aqueous solution dispersion of fluororesin powder (PTFE) to deposit the 
fluororesin on the skeletal portion of the nickel porous matter. Then, the 
fluororesin in an amount of 7.5% by weight was fixed to the skeletal 
portion of the nickel porous matter by heat treatment in the atmosphere of 
300.degree. C. to thereby prepare a support of a three-dimensional 
structure having a hydrophobic portion. FIGS. 2 and 3 are sectional views 
showing examples of negative electrodes constructed by using the support 
having hydrophobic property. FIG. 4 is a schematic view of an AA-size 
sealed nickel-hydrogen storage battery constructed by using these negative 
electrodes. The negative electrodes as shown in FIGS. 2 and 3 were 
respectively prepared as follows. Hydrogen absorbing alloy powder 5 using 
MmNi.sub.3.8 Mn.sub.0.4 Al.sub.0.3 Co.sub.0.5 with a theoretical capacity 
of 250 mAh/g and an average particle size of 12 .mu.m and water were mixed 
to prepare paste having a water content of about 20%. The aforementioned 
porous matter of a three-dimensional structure (thickness; 1.2 mm) having 
hydrophobic property was filled with the paste. After drying the paste, 
the porous matter was pressed into a thickness of 0.5 mm and cut into a 
size of 39 mm.times.80 mm, thereby preparing a negative electrode A having 
a porosity of 31% as shown in FIG. 2. On the other hand, a negative 
electrode was prepared in the same manner as the negative electrode A. 
PTFE powder was deposited on the surface of the negative electrode by 
using a spray coating instrument equipped with static generator. Then, the 
PTFE powder was fixed to the surface portion of the negative electrode by 
pressing. Then, the resulting negative electrode was cut into the same 
size as that of the negative electrode A, thereby preparing a negative 
electrode B as shown in FIG. 3. Consequently, the negative electrode B was 
coated with a PTFE powder layer 6 in an amount of 0.48 mg/cm.sup.2. As a 
comparative example, a negative electrode C was prepared in the same 
manner as the negative electrode A, except that the supporter of the 
negative electrode C was formed of a sponge-like nickel porous matter 
having a porosity of 95% without fluororesin deposited thereon. Then, by 
using the negative electrodes thus prepared, ten cells of AA-size sealed 
nickel-hydrogen storage batteries limited by the positive electrode 
capacity of 1000 mAh were respectively prepared to have a spiral structure 
constituted by a negative electrode 7, a known foamed metal type nickel 
positive electrode 8 and a separator 9 prepared by sulfonated 
polypropylene non-woven fabric and disposed between the negative electrode 
7 and the positive electrode 8 as shown in FIG. 4. The condition of the 
battery design was that the chargeable capacity of the negative electrode 
was established to be from 1.3 times to 1.4 times as much as that of the 
positive electrode. A KOH aqueous solution having specific gravity of 1.30 
and saturated with LiOH.H.sub.2 O was poured into the respective battery 
cases 10 by an amount of 2.2 cm.sup.3. The reference numeral 11 designates 
a gasket for insulating the edge of a sealing plate 14 and a positive 
electrode terminal cap 15 from the battery case 10. The reference numeral 
12 designates an insulating plate for insulating the inner bottom portion 
of the battery case from the lower portion of the spiral electrodes. The 
reference numeral 16 designates a positive electrode lead for electrically 
connecting the nickel positive electrode to the sealing plate. Although 
the safety vent is, in general, operated by pressure of 10 to 15 
kg/cm.sup.2, the safety vent 13 in this embodiment is established to be 
operated by pressure of not less than 30 kg/cm.sup.2 for the purpose of 
measuring the internal gas pressure of the battery. The internal gas 
pressure of the battery was measured as follows. After assembled, the 
battery was charged with 0.1 cmA for 15 hours in an atmosphere of 
20.degree. C., and then discharged with 0.2 cmA to 1.0 V. Then, a 1 mm 
.phi. hole was formed in the bottom portion of the battery case 10. The 
battery was fixed to an apparatus provided with a pressure sensor. The 
internal gas pressure of the battery was measured with the pressure sensor 
at the point of time when the battery was charged by 150% with the charge 
rate changed to various values. FIG. 5 shows the relation between the 
charge rate and the internal gas pressure of the battery with respect to 
the batteries respectively constituted by using the negative electrodes A, 
B and C. In FIG. 5 the symbols A, B and C show characteristics of the 
batteries using the negative electrodes A, B and C, respectively. In the 
comparative example C, the internal gas pressure of the battery was within 
a range of from 22 to 27 kg/cm.sup.2 when the battery was rapidly charged 
at 1 cmA. Accordingly, in an actual battery having a safety vent which is 
actuated to open by pressure of 10 to 15 kg/cm.sup.2, rapid charging is 
impossible. Compared with the battery using the negative electrode C, the 
batteries using the negative electrodes A and B were excellent in 
characteristics as shown by the symbols A and B in FIG. 5. In short, the 
internal gas pressure of the battery A was within a range of from 5 to 6.4 
kg/cm.sup.2 when the battery was charged at 1 cmA, and the internal gas 
pressure of the battery B was within a range of from 3 to 4 kg/cm.sup.2 
when the battery was charged at 1 cmA. Furthermore, in the cases of the 
batteries A and B, the battery internal pressure increased little 
regardless of repetition of charging/discharging 500 times. Consequently, 
the batteries A and B showed excellent characteristics, respectively. 
Although this example has shown the case where the fluororesin is disposed 
in the skeletal surface portion of the sponge-like nickel porous matter as 
a supporter of a three-dimension structure having hydrophobic property, 
the same effect can be attained as long as hydrophobic property can be 
given to selected one of porous or foam matters of resins, such as 
polypropylene, polyethylene, polyamide, ABS, polysulfone, poly(vinyl 
chloride) and the like, and hydrophobic porous supporter of carbon or 
nickel fibers. If the porosity of the nickel porous matter having a 
three-dimensional structure is not more than 90%, the capacity density of 
the negative electrode is lowered so that battery internal pressure 
increases when the battery is constructed under the conditions as 
described above. Accordingly, it is preferable that the porosity is not 
less than 80%. 
Further, if the weight per apparent unit area of the nickel porous matter 
becomes not less than 60 mg/ cm.sup.2, the porosity of the negative 
electrode prepared by filling the porous matter with the hydrogen 
absorbing alloy by a predetermined amount becomes not more than 28% to 
thereby increase battery internal pressure. If the weight becomes not more 
than 20 mg/cm.sup.2, on the contrary, mechanical strength of the nickel 
porous matter is lowered to make it difficult to fill the porous matter 
with the hydrogen absorbing alloy. If the porosity of the negative 
electrode becomes not more than 28%, the hydrogen gas absorbing reaction 
area thereof is lowered so that battery internal pressure increases. If 
porosity becomes not less than 35%, on the contrary, the capacity density 
of the negative electrode is lowered to make it impossible to construct a 
sealed battery of positive electrode capacity limitation. 
EXAMPLE 2 
An available sponge-like nickel porous matter having a porosity of 95% was 
dipped into an aqueous solution dispersion containing 70 part by weight of 
PTFE powder and 30 part by weight of palladium black powder capable of 
catalyzing the decomposition (H.sub.2 .fwdarw.2H) of hydrogen gas, to 
deposit the PTFE powder and the palladium black powder on the skeletal 
portion of the nickel porous matter in the ratio 70:30. Then the porous 
matter was heated at 300.degree. C. to prepare a support of a 
three-dimensional structure having a mixture of PTFE and palladium black 
at its skeletal portion. A negative electrode D was prepared by using the 
supporter in the same manner as in the Example 1. Then, a mixture of PTFE 
and palladium black in the ratio 70:30 was applied to the surface of the 
negative electrode D to prepare a negative electrode E having a layer of 
the mixture of PTFE and catalyst at its surface portion in the same manner 
as in the Example 1. On the other hand, a sponge-like nickel porous matter 
was dipped into an aqueous solution dispersion containing 70 part by 
weight of PTFE powder and 30 part by weight of acetylene black powder 
having electron conductivity, thereby depositing the mixture of PTFE 
powder and acetylene black powder on the skeletal portion of the nickel 
porous matter. Then, the porous matter was treated in an atmosphere of 
300.degree. C. to prepare a support of a three-dimensional structure 
having the mixture of PTFE and acetylene black at its skeletal portion. A 
negative electrode F was prepared by using this supporter in the same 
manner as in the Example 1. Then, a mixture of PTFE and palladium black in 
the weight ratio 70:30 was applied to the surface of the negative 
electrode F to prepare a negative electrode G having a layer of the 
mixture of PTFE and electron conductive matter at its surface portion in 
the same manner as in the Example 1. By using the negative electrodes (D, 
E, F and G), various batteries were prepared in the same manner as in the 
Example 1. The values of battery internal pressure of the batteries at the 
point of time when the respective battery was charged by 150% with 1 cmA 
are shown in Table 1. The results of the batteries A, B and C in the 
Example 1 are also shown in the Table 1. 
TABLE 1 
______________________________________ 
Negative Capacity 
Battery 
Electrode Internal Gas Pressure 
Ratio 
______________________________________ 
A A 5 .about. 6.4 kg/cm.sup.2 
74 .about. 76% 
B B 3 .about. 4 kg/cm.sup.2 
72 .about. 75% 
C C 22 .about. 27 kg/cm.sup.2 
80 .about. 83% 
D D 4 .about. 5.2 kg/cm.sup.2 
79 .about. 82% 
E E 2 .about. 2.8 kg/cm.sup.2 
80 .about. 83% 
F F 5 .about. 7 kg/cm.sup.2 
79 .about. 82% 
G G 3 .about. 5 kg/cm.sup.2 
79 .about. 83% 
______________________________________ 
Further, the discharge characteristic in each of the batteries using the 
negative electrodes A to G was examined. In the Table 1, the discharge 
characteristic is expressed as a capacity ratio [capacity ratio=(the 
capacity when discharged with 3 cmA)/(the capacity when discharged with 
0.2 cmA).times.100%] of the capacity when each battery was discharged with 
3 cmA to 1.0 V to the capacity when discharged with 0.2 cmA to 1.0 V after 
charged in an atmosphere of 20.degree. C. The larger the value of the 
capacity ratio, the more excellent the discharge characteristic. The 
values of internal gas pressure of the respective batteries using the 
negative electrodes D and E were within a range of from 4 to 5.2 
kg/cm.sup.2 and within a range of from 2 to 2.8 kg/cm.sup.2, respectively. 
In the cases of the negative electrodes D and E, the battery internal 
pressure was reduced because of the presence of palladium black capable of 
catalyzing the decomposition of a hydrogen gas, compared with the cases of 
the negative electrodes A and B. In short, the batteries using the 
negative electrodes D and E showed excellent characteristics. The values 
of internal gas pressure of the batteries F and G using the sponge-like 
nickel porous matter having the mixture of acetylene black and PTFE at its 
skeletal portion were excellent similarly to the values of internal gas 
pressure of the batteries A and B. On the contrary, the discharge 
characteristic of the battery C using the negative electrode C as a 
comparative example was so good that the capacity ratio was from 80 to 
83%. The capacity ratio of the batteries using the negative electrodes A 
and B were within a range of from 74 to 76% and within a range of from 72 
to 75%, respectively, the values being slightly lower than the value in 
the case of the negative electrode C. This is because the surface portion 
of the nickel porous matter having electron conductivity was coated with 
PTFE having little electron conductivity. In other words, this is because 
the contacting area between the hydrogen absorbing alloy powder and the 
skeleton of nickel decreased. On the other hand, the discharge 
characteristics of the batteries F and G using the supporter having the 
mixture of PTFE and acetylene black at its skeletal portion were within a 
range of from 79 to 82% and within a range of from 79 to 83%, 
respectively, the values being excellent similarly to the value in the 
case of the battery C. Also the discharge characteristics of the batteries 
D and E showed values similar to the value in the case of the battery C. 
This is because acetylene black having electron conductivity and palladium 
black having both catalystic property and electron conductivity existed in 
the surface portion of the skeleton of nickel. 
Although this example has shown the case where palladium black is used as a 
material capable of catalyzing the decomposition of a hydrogen gas, the 
same effect can be attained even in the case where another catalyst, such 
as platinum, platinum carrying carbon, palladium carrying carbon or the 
like, is used. Although this example has shown the case where acetylene 
black is used as a material having electron conductivity, the same effect 
can be attained even in the case where another material having electron 
conductivity, such as nickel powder, carbon black or the like, is used. 
Further, the portion having hydrophobic property may be formed of a 
mixture of PTFE, a catalystic material and a conductive material. 
EXAMPLE 3 
A supporter formed of a sponge-like nickel porous matter having hydrophobic 
property in the same manner as in the Example 1 was filled with paste 
prepared by mixing hydrogen absorbing alloy powder having a mean particle 
diameter of 12 .mu.m and represented by the formula MmNi.sub.3.8 
Mn.sub.0.4 Al.sub.0.3 Co.sub.0.5 and a polyvinyl alcohol aqueous solution 
as a hydrophilic material. While the polyvinyl alcohol concentration of 
the aqueous solution was changed, negative electrodes H, I, J and K were 
prepared in the same manner as the negative electrode A in the Example 1. 
The negative electrodes H, I, J and K contained polyvinyl alcohol by 
amounts of 0.02 wt %, 0.18 wt %, 0.25 wt % and 0.3 wt %, respectively. 
Then, a PTFE layer was formed on each of the negative electrodes prepared 
in the same manner as the negative electrodes H, I, J and K, thereby 
preparing negative electrodes L, M, N and O. By using these negative 
electrodes, various batteries were prepared in the same manner as in the 
Example 1 (except that the safety vent in each of the batteries was set to 
be actuated to open by pressure of 12 kg/cm.sup.2). The internal gas 
pressure and charge/ discharge cycle life were examined. The cycle life 
test was conducted under the condition that the battery was charged with 1 
cmA for 1.5 hours in an atmosphere of 20.degree. C. and then discharged 
with 1 cmA until the terminal voltage reached 1.0 V. The discharge 
capacity in each cycle was examined in the cycle life test. The 
measurement condition of battery internal pressure was the same as in the 
Example 1. The internal gas pressure of the batteries using various 
negative electrodes and the cycle number when the discharge capacity was 
reduced by 10% relative to the initial capacity are shown in Table 2. 
Further, the characteristics of the batteries using the negative 
electrodes A and B containing no polyvinyl alcohol are also shown in the 
Table 2. The internal pressure in each of the batteries H, I, J, L, M and 
N using negative electrodes containing polyvinyl alcohol by the amounts of 
0.02 wt %, 0.18 wt % and 0.25 wt % was excellent similarly to that in each 
of the batteries A and B using negative electrodes containing no polyvinyl 
alcohol. However, the internal pressure in each of the batteries K and O 
using negative electrodes containing polyvinyl alcohol by an amount of 0.3 
wt % was increased compared with that in each of the batteries A and B. 
Accordingly, it is preferable that the negative electrode contains 
polyvinyl alcohol by an amount of not more than 0.25 wt %. On the other 
hand, the cycle life in each of the batteries H, I, J, L, M and N was 
improved compared with that in each of the batteries A and B. This is 
because hydrophobic polyvinyl alcohol existing in the negative electrode 
keeps the electrolyte in the negative electrode regardless of expansion of 
the position electrode caused by repetition of charge/discharge cycles. On 
the other hand, the cycle life in each of the batteries K and L was short. 
This is because the surfaces of the alloy particles are covered with 
polyvinyl alcohol to thereby reduce the hydrogen absorbing capacity and 
increase the battery internal pressure, so that the safety vent is 
actuated to thereby reduce the discharge capacity. Accordingly, it is 
preferable that the negative electrode contains polyvinyl alcohol by an 
amount within a range of from 0.02 to 0.25 wt %. 
Although this example has shown the case where polyvinyl alcohol is used as 
a hydrophilic material, the same effect can be attained even in the case 
where another hydrophilic material, such as carboxymethylcellulose, 
methylcellulose or the like, is used. 
TABLE 2 
__________________________________________________________________________ 
Concentration of 
hydrophobic 
polyvinyl alcohol 
Negative 
in negative elec 
Internal 
Battery 
Electrode 
trode Gas pressure 
Cycle Life 
__________________________________________________________________________ 
A A 0 wt % 5 .about. 6.4 kg/cm.sup.2 
450 .about. 500 cycles 
B B 0 wt % 3 .about. 4 kg/cm.sup.2 
450 .about. 500 cycles 
H H 0.02 
wt % 5 .about. 6.4 kg/cm.sup.2 
480 .about. 520 cycles 
I I 0.18 
wt % 5 .about. 6.4 kg/cm.sup.2 
500 .about. 550 cycles 
J J 0.25 
wt % 5.5 .about. 7 kg/cm.sup.2 
500 .about. 550 cycles 
K K 0.3 
wt % 9 .about. 12 kg/cm.sup.2 
200 .about. 300 cycles 
L L 0.02 
wt % 3 .about. 4 kg/cm.sup.2 
480 .about. 520 cycles 
M M 0.18 
wt % 3 .about. 4 kg/cm.sup.2 
500 .about. 550 cycles 
N N 0.25 
wt % 3.5 .about. 5 kg/cm.sup.2 
500 .about. 550 cycles 
O O 0.3 
wt % 8 .about. 12 kg/cm.sup.2 
200 .about. 300 cycles 
__________________________________________________________________________ 
EXAMPLE 4 
Negative electrodes P, Q, R, S, T and U were prepared in the same manner as 
the negative electrode B in the Example 1 while the quantity of PTFE to be 
applied to the surface thereof was changed variously. By using the 
negative electrodes P, Q, R, S, T and U, various batteries were prepared 
in the same manner as in the Example 1. The internal gas pressure in each 
of the batteries was examined. The results of examination are shown in 
Table 3. 
TABLE 3 
______________________________________ 
Negative Surface Coating 
Internal Gas 
Battery 
Electrode Amount of PTFE 
Pressure 
______________________________________ 
P P 0.1 mg/cm.sup.2 
5 .about. 6 Kg/cm.sup.2 
Q Q 0.15 mg/cm.sup.2 
4 .about. 5 Kg/cm.sup.2 
R R 0.5 mg/cm.sup.2 
3 .about. 4 Kg/cm.sup.2 
S S 1.0 mg/cm.sup.2 
3 .about. 4 Kg/cm.sup.2 
T T 1.5 mg/cm.sup.2 
4 .about. 5 Kg/cm.sup.2 
U U 2.0 mg/cm.sup.2 
7 .about. 9 Kg/cm.sup.2 
______________________________________ 
The internal pressure in each of the batteries Q, R, S and T using the 
negative electrodes respectively coated with PTFE by amounts of 0.15 
mg/cm.sup.2, 0.5 mg/cm.sup.2, 1.0 mg/cm.sup.2 and 1.5 mg/cm.sup.2 was not 
more than 5 kg/cm.sup.2 and was very excellent. On the other hand, the 
internal gas pressure of the battery P using the negative electrode coated 
with PTFE by an amount of 0.1 mg/cm.sup.2 was similar to that of the 
battery A in the Example 1. In the battery P, there was no effect by the 
coating of PTFE on the surface of the negative electrode. The internal gas 
pressure of the battery U using the negative electrode coated with PTFE by 
an amount of 2.0 mg/cm.sup.2 was increased to be within a range of from 7 
to 9 kg/cm.sup.2. This is because the hydrophobic resin in the surface of 
the negative electrode increases to suppress absorption of the electrolyte 
into the negative electrode to thereby deteriorate charge efficiency of 
the negative electrode. Accordingly, it is preferable that the quantity of 
PTFE deposited on the surface portion of the negative electrode is within 
a range of from 0.15 to 1.5 mg/cm.sup.2. 
EXAMPLE 5 
Various negative electrodes V, W, X and Y were prepared in the same manner 
as the negative electrode A in the Example 1, except that the temperature 
for heat treatment after deposition of PTFE was changed variously to 
150.degree. C., 200.degree. C., 400.degree. C. and 450.degree. C. By using 
the negative electrodes thus prepared, various batteries were prepared. 
The battery internal pressure and cycle life (under the condition that the 
operation pressure of the safety vent used in the cycle life test was 12 
kg/cm.sup.2) were examined in the same manner as in the Examples 1 and 3. 
The results of examination are shown in Table 4. The characteristics of 
the battery using the negative electrode A in the Example 1 were also 
shown in the Table 4. 
TABLE 4 
______________________________________ 
Heat- 
Negative treatment 
Bat- Elec- Tempera- Internal Gas 
tery trode ture Pressure Cycle life 
______________________________________ 
V V 150.degree. C. 
10 .about. 12 Kg/cm.sup.2 
200 .about. 250 cycles 
W W 200.degree. C. 
5 .about. 6.4 Kg/cm.sup.2 
450 .about. 480 cycles 
A A 300.degree. C. 
5 .about. 6.4 Kg/cm.sup.2 
450 .about. 500 cycles 
X X 400.degree. C. 
5 .about. 6.4 Kg/cm.sup.2 
480 .about. 530 cycles 
Y Y 450.degree. C. 
10 .about. 12 Kg/cm.sup.2 
250 .about. 300 cycles 
______________________________________ 
Each of the batteries W, A and X using the supports prepared by the steps 
of depositing PTFE on the skeletal portion of the sponge-like nickel 
porous matter, and heat-treating the porous matter at a temperature of 
200.degree. to 400.degree. C., was excellent in battery internal pressure 
and cycle life. On the other hand, the internal gas pressure of the 
battery V using the supporter subjected to be within a range of from 10 to 
12 kg/cm.sup.2. Further, the cycle life of the battery V was within a 
range of from 200 to 250 cycles. Consequently, the characteristics of the 
battery V were deteriorated. This is because PTFE could not be 
sufficiently fixed to the skeletal surface portion of the nickel porous 
matter when the temperature for heat treatment was 150.degree. C., so that 
PTFE was dropped out of the skeleton during the impregnating of the porous 
matter with the paste or with repetition of charge/discharge cycles to 
thereby reduce hydrophobic property of the negative electrode. On the 
contrary, when the temperature for heat treatment reached 450.degree. C. 
as shown in the battery Y, PTFE was partly decomposed to thereby reduce 
hydrophobic property of the negative electrode and shorten the cycle life. 
Accordingly, it is preferable that the temperature for heat treatment is 
to be within a range of from 200.degree. to 400.degree. C. 
Next, a negative electrode Z in which PTFE was coated on the surface of the 
negative electrode but not fixed by pressing was prepared in the same 
manner as the negative electrode B in the Example 1. By using the negative 
electrode Z, a battery was prepared in the same manner as in the Example 
1. The internal gas pressure and cycle life of the battery thus prepared 
were examined. The internal gas pressure of the battery using the negative 
electrode Z was within a range of from 3 to 4 kg/cm.sup.2 and was 
excellent similarly to that of the battery B in the Example 1. However, 
the internal gas pressure of the battery was increased with repetition of 
charge/ discharge cycles. When charge/discharge was repeated by 400 
cycles, the internal gas pressure of the battery became not less than 12 
kg/cm.sup.2 to operate the safety vent to make a gas and the electrolyte 
escape to thereby reduce the discharge capacity. This is because PTFE was 
not sufficiently fixed to the surface portion of the negative electrode so 
that PTFE was dropped out of the surface portion of the negative electrode 
with repetition of charge/discharge cycles. 
As described above, according to the present invention, in a sealed 
alkaline storage battery comprising a positive electrode constituted 
mainly by a metal oxide, a negative electrode constituted mainly by a 
hydrogen absorbing alloy capable of absorbing/desorbing hydrogen acting as 
an active material and a supporter for supporting said alloy, an alkaline 
electrolyte, and a separator, an effect to enable rapid charging (1 cmA) 
to be performed can be obtained by making the supporter to have a 
three-dimensional structure having hydrophobic property. Further, an 
effect to enable more rapid charging (2 cmA) to be performed can be 
obtained by providing a portion having hydrophobic property on a surface 
portion of the negative electrode. 
Further, in the method of producing a negative electrode for the 
above-mentioned sealed alkaline storage battery, it is possible to obtain 
an effect that a sealed alkaline storage battery capable of being subject 
to rapid charging and excellent in cycle life against repetition 
charge/discharge can be produced by employing the steps of: depositing a 
fluororesin on a skeletal portion of a nickel porous matter having a 
three-dimensional structure; fixing the fluororesin to the skeletal 
portion of the nickel porous matter by heat treatment at a temperature 
lower than the temperature of decomposition of the fluororesin to thereby 
prepare a support having a hydrophobic portion; and preparing a negative 
electrode through filling the supporter with paste mainly containing a 
hydrogen absorbing alloy, drying the paste and then pressing/cutting the 
support into predetermined thickness and size.