U.S. patent application number 09/884613 was filed with the patent office on 2001-11-08 for process for producing hydrogen absorbing alloy powder and hydrogen absorbing alloy electrode.
This patent application is currently assigned to Shin-Etsu Chemical Co., Ltd.. Invention is credited to Ishii, Masatoshi, Shinya, Naofumi, Sugahara, Hiroto.
Application Number | 20010037843 09/884613 |
Document ID | / |
Family ID | 13494591 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010037843 |
Kind Code |
A1 |
Shinya, Naofumi ; et
al. |
November 8, 2001 |
Process for producing hydrogen absorbing alloy powder and hydrogen
absorbing alloy electrode
Abstract
Provided is an inexpensive process for producing hydrogen
absorbing alloy powder suitable for a nickel-metal hydride storage
battery having a high rate discharge property, a high capacity and
a long cycle life for repetition of charge and discharge. The
process comprises a step of an addition of a rare earth metal oxide
and/or hydroxide to a hydrogen absorbing alloy powder, a wet or dry
mixing step and a thermal treatment step in an inert atmosphere or
in a vacuum.
Inventors: |
Shinya, Naofumi; (Fukui-ken,
JP) ; Sugahara, Hiroto; (Fukui-ken, JP) ;
Ishii, Masatoshi; (Fukui-ken, JP) |
Correspondence
Address: |
Henry D. Coleman
Coleman Sudol Sapone, P.C.
714 Colorado Avenue
Bridgeport
CT
06605-1601
US
|
Assignee: |
Shin-Etsu Chemical Co.,
Ltd.
|
Family ID: |
13494591 |
Appl. No.: |
09/884613 |
Filed: |
June 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09884613 |
Jun 19, 2001 |
|
|
|
09265682 |
Mar 10, 1999 |
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Current U.S.
Class: |
148/429 ;
75/351 |
Current CPC
Class: |
H01M 10/345 20130101;
C01B 3/0057 20130101; Y10S 420/90 20130101; H01M 4/383 20130101;
Y02P 70/50 20151101; Y02E 60/32 20130101; Y02E 60/10 20130101; C22C
32/0026 20130101; B22F 2998/10 20130101; B22F 2998/10 20130101;
B22F 9/023 20130101; B22F 1/0003 20130101 |
Class at
Publication: |
148/429 ;
75/351 |
International
Class: |
C22C 019/03; B22F
009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 1998 |
JP |
072619/1998 |
Claims
1. Process for producing a hydrogen absorbing alloy powder
comprising an addition step of a rare earth metal oxide and/or
hydroxide to a hydrogen absorbing alloy powder, a wet or dry mixing
step, and a thermal treatment step at 100 to 800.degree. C. in an
inert atmosphere or in a vacuum.
2. Process for producing a hydrogen absorbing alloy powder
according to claim 1 wherein said hydrogen absorbing powder before
the addition of the rare earth metal oxide and/or hydroxide is
obtained starting from an ingot of hydrogen absorption alloy
through steps comprising a thermal treatment at 800 to 1100.degree.
C. in an inert atmosphere or in a vacuum, a cooling step, and then
a milling step.
3. Process for producing a hydrogen absorbing alloy is powder
according to claim 1 wherein said hydrogen absorbing powder before
the addition of the rare earth metal oxide and/or hydroxide is
represented by a general formula
(R).sub.n(Ni).sub.5-x-y-z-(Mn).sub.x(Al).sub.y(Co).sub.z wherein R
is La alone or a mixture of La and one or more rare earth elements
other than La, and n, x, y and z are each a positive number,
denotes a atomic ratio satisfying 0.93.ltoreq.n.ltoreq.1.06,
0<x.ltoreq.0.6, 0<y.ltoreq.0.6 and 0<z.ltoreq.1.0.
4. Process for producing a hydrogen absorbing alloy powder
according to claim 1 wherein said rare earth metal oxide and/or
hydroxide is added in an amount of 0.1 to 20% by weight toward the
hydrogen absorbing alloy.
5. Process for producing a hydrogen absorbing alloy powder
according to claim 1 wherein said rare earth metal oxide and/or
hydroxide is oxide and/or hydroxide of at least one selected from
the group consisting of Gd, Ho, Er, Yb and Y, or compound oxide
and/or compound hydroxide of at least two selected from said
group.
6. A hydrogen absorbing alloy electrode for a nickel-metal hydride
storage battery formed of the hydrogen absorbing alloy powder
produced according to claim 1.
7. A hydrogen absorbing alloy electrode for a nickel-metal hydride
storage battery formed of the hydrogen absorbing alloy powder
produced according to claim 2.
8. A hydrogen absorbing alloy electrode for a nickel-metal hydride
storage battery formed of the hydrogen absorbing alloy powder
produced according to claim 3.
9. A hydrogen absorbing alloy electrode for a nickel-metal hydride
storage battery formed of the hydrogen absorbing alloy powder
produced according to claim 4.
10. A hydrogen absorbing alloy electrode for a nickel-metal hydride
storage battery formed of the hydrogen absorbing alloy powder
produced according to claim 5.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a process for producing
hydrogen absorbing alloy powder suitable for a negative electrode
of an alkaline storage battery, as well as a hydrogen absorbing
alloy electrode formed of the hydrogen absorbing alloy powder
produced thereby. More specifically, it relates to a process for
producing a hydrogen absorbing alloy suitable to the application of
a nickel-hydrogen storage battery which excels in properties such
as a cycle life and a high rate discharge property.
[0003] 2. Description of the Related Art
[0004] Since a hydrogen absorbing alloy which can charge and
discharge hydrogen was discovered, the application thereof has been
progressively developed. An alkaline storage battery containing a
negative electrode formed of the hydrogen absorbing alloy has been
made practicable, and the hydrogen absorbing alloy used for it has
been improved one after another.
[0005] Although the LaNi.sub.5 alloy investigated initially
(Japanese Provisional Patent Publication No. 51-13934/1976) has an
advantage that the absorbed amount of hydrogen is large, it also
has disadvantages such as expensive La metal and a tendency to
become impalpable powder in progress of repetition of charge and
discharge of hydrogen. Further, it has such a disadvantage that it
is easily corroded by an alkaline solution or an acid solution.
Accordingly, when said hydrogen absorbing alloy is applied in an
alkaline storage battery, despite an high initial capacity, the
capacity becomes no more than a half of the initial capacity after
the 50 or more times of charge and discharge cycles. Consequently,
the hydrogen absorbing alloy has an disadvantage of being incapable
of withstanding a longer period of use.
[0006] The disadvantages have been improved by substituting a part
of La of the LaNi.sub.5 alloy by Ce, Pr, Nd or other rare earth
elements, and/or by substituting a part of Ni of the LaNi.sub.5
alloy by metal such as Co, Al, Mn or the like (Japanese Provisional
Patent Publication Nos. 53-48918/1978, 54-64014/1979,
60-250558/1985, 61-91862/1986, and 61-233969/1986).
SUMMARY OF THE INVENTION
[0007] The hydrogen absorbing alloy having Mm has an advantage that
Mm is inexpensive. As the applications for the hydrogen absorbing
alloy have been expanded widely recently, however, the hydrogen
absorbing alloy having Mm which also owns a good high rate
discharge property has been sought.
[0008] In order to improve the high rate discharge property, a
surface treatment or alloy (an alkaline treatment or an acid
treatment), a plating treatment, or an addition of B (boron), Mo or
others have been carried out conventionally. However, it is
difficult to maintain the surface activity of the alloy in use of
the surface treatment such as the alkaline or the acid treatment,
or in the addition of the other element.
[0009] Hence, it is the first object of the present invention to
provide an inexpensive process for producing hydrogen absorbing
alloy powder suitable for a nickel-metal hydride storage battery
having a excellent high rate discharge property.
[0010] Moreover, it is the second object of the present invention
to provide an inexpensive process for producing hydrogen absorbing
alloy powder suitable for a nickel-metal hydride storage battery
having a higher capacity and a longer cycle life for repetition of
charge and discharge, as well as an excellent high rate discharge
property.
[0011] In above view, the present inventors have studied the
problems and found that the cycle life and the high rate discharge
property can be improved by adding a rare earth metal oxide and/or
hydroxide to a hydrogen absorbing alloy powder, then wet- or
dry-mixing them, and subsequently treating thermally in an inert
atmosphere or in a vacuum. Thus, the present invention has been
completed.
[0012] According to the present invention, an ingot of hydrogen
absorbing alloy is thermally treated at the temperature of 800 to
1100.degree. C. in an inert atmosphere or in a vacuum, then cooled,
and reduced to yield a hydrogen absorbing alloy powder. A rare
earth metal oxide or hydroxide is added to the obtained hydrogen
absorbing alloy powder, and a wet- or dry-mixed. Then, they are
further thermally treated at 100 to 800.degree. C. in an inert
atmosphere or in a vacuum. As a result, a storage battery having an
excellent high rate discharge property is obtained, since the
surface activity of the obtained hydrogen absorbing alloy powder is
not damaged by an alkaline electrolyte.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0013] The present invention relates a process for producing
hydrogen absorbing alloy powder, comprising steps of adding a rare
earth metal oxide and/or hydroxide to a hydrogen absorbing alloy
powder, preferably to the hydrogen absorbing alloy powder obtained
by a thermal treatment of an ingot of hydrogen absorbing alloy at
the temperature of 800 to 1100.degree. C. in an inert atmosphere or
in a vacuum, then cooling, and pulverization; mixing the resultant
in a wet or dry manner; and then further thermally treating the
mixture in an inert atmosphere or in a vacuum.
[0014] Compositions or preparation methods for hydrogen absorbing
alloy which can be used in the present invention are not
particularly limited. It is preferably the intermetallic compound
represented stoichiometrically by LaNi.sub.5, wherein a part of La
is substituted by Ce, Pr, Nd or the other rare earth element and a
part of Ni is substituted by Co, Mn, Al or the other element such
as Fe, Cu, Si, Ti, Mo or Zr. In view of improving the cycle life,
it is more preferable to substitute at least a part of Ni by Mn,
further more preferable to substitute at least a part of Ni by Mn
and Co.
[0015] According to the present invention, the hydrogen absorbing
alloy having the said compositions can be used. And MmNi.sub.5-type
hydrogen absorbing alloy having the following composition is
preferably used. It is represented specifically by the general
formula, (R).sub.n(Ni).sub.5-x-y-z(Mn).sub.x(Al).sub.y(Co).sub.z;
wherein R is La or a mixture of La and at least one rare earth
element (selected from Ce, Pr, Nd or the like); n, x, y and z are
each a positive number which represents an atomic ratio; and n is
between 0.93 and 1.06, and x, y and z each satisfies
0<x.ltoreq.0.6, 0<y.ltoreq.0.6 and 0<z.ltoreq.1.0.
[0016] Furthermore, other than the above composition, the
compositions having a part of Ni substituted by Fe, Si, Cu, Mo, Ti,
Zr or the like may be used. Among them, the compositions having 20%
by weight or more of La in R are more preferable.
[0017] Although the preparation method for the ingot of hydrogen
absorbing alloy is not limited, the casting of the liquid having
each of metal components melted is preferable because of lower
cost. Even when other methods including a roll rapid quenching
method and an atomization method are used, the hydrogen absorbing
alloys obtained may bring the same effects as or better effects
than those obtained from the casting.
[0018] According to the present invention, the ingot of hydrogen
absorbing alloy may be thermally treated. Although any one of the
known methods of thermal treatments may be selectively used, it is
preferable to use the treatment at 800 to 1100.degree. C. for 5 to
20 hours in resistance-type furnace in a vacuum or in an inert
atmosphere such as argon, helium or the like. The thermal treatment
effects the removal of segregation and strain of metals in the
alloy. If the temperature is less than 800.degree. C., the removal
of segregation of metals in the alloy may not be enough. If the
temperature is more than 1100.degree. C., the discrepancy in the
composition may take place since metals having higher vapor
pressures such as Mn come out. Accordingly, the temperature range
of 800 to 1100.degree. may be used.
[0019] The atmosphere of an inert gas such as argon or helium is
used for eliminating the contamination by impurities such as
oxygen. Accordingly, as long as the contamination is eliminated,
any other methods may be used. That is, it is not limited to the
inert atmosphere. A vacuum may be used in the same reason and not
limited to the vacuum in the strict sense in the same reason. The
"in a vacuum" is generally under the pressure of about 10.sup.-4
Torr.
[0020] The ingot of hydrogen absorbing alloy obtained in the
above-mentioned methods is reduced to a powder with the average
particle diameter 5 to 100 .mu.m, preferably 15 to 60 .mu.m to by a
hydration milling or a milling using a ball mill, a jet mill, a
pulvelizer or the like.
[0021] The present invention provides a method for forming islands
of rare earth metal oxide and/or hydroxide on the surface of the
alloy described above and also forming a nickel-rich layer having a
higher Ni concentration than the mother phase, and/or a cobalt-rich
layer having a higher Co concentration than the mother phase within
500 nm in the depth from the surface of the alloy. In a specific
method, rare earth metal oxide and/or hydroxide which has a lower
oxidation-reduction potential than both of Co and Ni and which has
an oxidation-reduction potential of -2.0V or more may be added to
the hydrogen absorbing alloy powder.
[0022] Oxide and/or hydroxide of a metal such as Cu or Pb having a
higher oxidation-reduction potential than both of Co and Ni, may
unpreferably increase the elution of Co and the like.
[0023] Rare earth metal oxide or hydroxide may be used alone or as
a mixture thereof according to the present invention. Oxide and/or
hydroxide of rare-earth metal selected from the group consisting of
La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y may be
used. The metal oxide and hydroxide may be commonly expressed by
the general formulae R".sub.2O.sub.3 and R"(OH).sub.3,
respectively, wherein R" represents a rare earth element. However,
the metal oxide and hydroxide are not limited to those of general
formulas and include others which are not represented by the
general formulas.
[0024] The examples includes La.sub.2O.sub.3, CeO.sub.2,
Pr.sub.6O.sub.11, Nd.sub.2O.sub.3, Sm.sub.2O.sub.3,
Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Tb.sub.4O.sub.3, Dy.sub.2O.sub.3,
Ho.sub.2O.sub.3, Er.sub.2O.sub.3, Tm.sub.2O.sub.3, Yb.sub.2O.sub.3,
Lu.sub.2O.sub.3, Y.sub.2O.sub.3, La(OH).sub.3, Ce(OH).sub.3,
Pr(OH).sub.3, Nd(OH).sub.3, Sm(OH).sub.3, Eu(OH).sub.3,
Gd(OH).sub.3, Tb(OH).sub.3, Dy(OH).sub.3, Ho(OH).sub.3,
Er(OH).sub.3, Tm(OH).sub.3, Yb(OH).sub.3, Lu(OH).sub.3,
Y(OH).sub.3.
[0025] Oxide or hydroxide of rare earth metal selected from Gd, Ho,
Er, Yb and Y may be more preferably used.
[0026] In this specification, rare earth metal oxide includes
compound oxide of rare earth metals and rare earth metal hydroxide
includes compound hydroxide of rare earth metals. That is, the rare
earth metal oxide or hydroxide may be compound oxide or hydroxide
composed of two or more rare earth elements. Compound oxide or
hydroxide composed of two or more rare earth elements selected from
the group consisting of Gd, Ho, Er, Yb and Y may be preferable.
[0027] According to the present invention, compound oxide and/or
hydroxide, a combination of the rare earth metal oxide and/or
hydroxide describe above may be used. The compound oxide or
hydroxide is not a mixture of metal oxides or hydroxides but a
solid solution wherein metal oxides or hydroxides are
solution-treated. For example, it is expressed by the general
formula (R.sup.1).sub.a.multidot.(R.sup.2).sub.b or
(R.sup.1).sub.c.multidot.(R.sup.2).sub.d.multidot.(R.sup.3).sub.e,
using two or more of rare earth metal oxides or hydroxides
described above. In the general formula, R.sup.1, R.sup.2 and
R.sup.3 each is said rare earth metal oxide or hydroxide; a and b
each is a number between 0.1 and 0.9 with a proviso that a+b=1;
c,d,e each is a number between 0.1 and 0.8 with a proviso that
c+d+e=1.
[0028] Preferable examples includes
(Yb.sub.2O.sub.3).sub.a.multidot.(Lu.s- ub.2O.sub.3).sub.b,
(Yb.sub.2O.sub.3).sub.a.multidot.(Er.sub.2O.sub.3).sub- .b,
(Er.sub.2O.sub.3).sub.d.multidot.(Dy.sub.2O.sub.3).sub.b,
(Yb.sub.2O.sub.3).sub.c.multidot.(Sm.sub.2O.sub.3).sub.d.multidot.(Cd.sub-
.2O.sub.3).sub.e, (Y2O.sub.3).sub.c
.multidot.(Er.sub.2O.sub.3).sub.d.mult-
idot.(Yb.sub.2O.sub.3).sub.e,
(Yb(OH).sub.3).sub.a.multidot.(Er(OH).sub.3)- .sub.b,
(Er(OH).sub.3).sub.a.multidot.(Dy(OH).sub.3).sub.b.
[0029] According to the present invention, a mixture of said oxides
and/or hydroxides may be used. And other than oxides and/or
hydroxides of said rare earth metals, oxide or hydroxide of the
metal such as Mn, Al, V, Nb, Hf, Fe or Si which has lower
oxidation-reduction potential than both of Co and Ni may be
used.
[0030] Rare earth metal oxide and/or hydroxide (including compound
oxide and/or compound hydroxide) is added in the total amount of
0.1 to 20% by weight, preferably 0.1 to 10% by weight, more
preferably 0.1 to 2% by weight to the hydrogen absorbing alloy. If
less than 0.1% by weight to the alloy is added, the resulting
hydrogen absorbing alloy may worsen corrosion resistance, hydrogen
chargability and dischargability, or cycle life. If more than 20%
by weight to the alloy is added, thermal conduction or electric
conduction may be worsened since the contacts among the resulting
alloys are decreased, so that the production cost may also be
increased.
[0031] According to the present invention, following the addition
of rare earth metal oxide and/or hydroxide, the resultant is
wet-mixed or dry-mixed, and then thermally treated in an inert
atmosphere or in a vacuum to yield the alloy having islands of rare
metal oxide or hydroxide on the surface thereof.
[0032] Mixing the rare-metal oxide or hydroxide with the hydrogen
absorbing alloy is done in a wet or dry manner. In the wet-mixing,
water, hexane, acetone or the like may be added to the mixture of
the alloy powder and the rare earth metal oxide and/or hydroxide to
be stirred in a preferable period of 0.1 to 2 hours. In the
dry-mixing, the alloy powder and rare earth metal oxide and/or
hydroxide may be stirred for 0.1 to 2 hours in an inert atmosphere
such as argon or helium or in a vacuum.
[0033] According to the present invention, following the addition
and mixing of rare earth metal oxide and/or hydroxide, the thermal
treatment takes place at the temperature of 100 to 800.degree. C.,
preferably 200 to 500.degree. C., in an inert atmosphere of argon,
helium or the like or in a vacuum (about 1.times.10.sup.-4 Torr) or
in mixed gases of an inert gase and a small amount of H.sub.2O.
Accordingly, the rare earth metal oxide or hydroxide is attached
strongly to the alloy surface, forming islands on the alloy
surface. Hence, the metal oxide or hydroxide is not incorporated
into the binder from the alloy surface in the pasting step, staying
on the alloy surface unlike what is obtained without the thermal
treatment. Accordingly, when it is used as a negative electrode,
the corrosion resistance is enhanced since the rare earth metal
oxide or hydroxide stays on the alloy surface.
[0034] If the temperature is less than 100.degree. C., the
formation of the Ni-rich or Co-rich layer on the alloy surface may
not be enough, and if the temperature is more than 800.degree. C.,
oxidation of the alloy surface may go on to make the alloy surface
inert. Accordingly, the thermal treatment is carried out between
100 and 800.degree. C.
[0035] The reason why an inert gas atmosphere such as argon, helium
or the like, or a vacuum is used is same as described above.
Accordingly, any method in which the requirement can be satisfied
can be used without limiting the inert gas atmosphere such as argon
or the vacuum.
[0036] The binder for producing an electrode, which is added to the
obtained hydrogen absorbing alloy powder having islands of rare
earth oxide or hydroxide on the surface thereof, is not
particularly limited. The binder may be suitably selected from the
group consisting of polyvinyl alcohol, celluloses such as methyl
cellulose, carboxymethyl cellulose and the like and organic binder
such as PTFE, polyethylene oxide, polymeric latex and the like, and
may be used alone or as a mixture thereof. The binder in the amount
of 0.1 to 20% by weight to the alloy powder is added.
[0037] According to the present invention, a conductor which will
be filled with a mixture of the alloy and the binder or which a
mixture of the alloy and the binder is applied to, is not
particularly limited. The conductor may be selected suitably from
the group consisting of a three-dimensional conductor such as
nickel fibers, foamed nickel or the like, and a two-dimensional
conductor such as punched metal or the like.
[0038] The hydrogen absorbing alloy electrode may be produced as
follows. The hydrogen absorbing alloy powder treated according to
the present invention is added to the aqueous solution containing
said binder and kneaded to prepare the paste. The resulting paste
is applied to the surface of the conductor and dried, and pressed
to yields a hydrogen absorbing alloy electrode. In another process,
the paste is molded to a sheet, which is pressed to the conductor
surface to yield a hydrogen absorbing alloy electrode.
[0039] The present invention will be described further in details
using Examples. However, the present invention is not constrained
to these examples.
EXAMPLES 1 and 2
[0040] Ni, Co, Mn and Al each was weighed so as to be 3.70, 0.80.
0.20 and 0.30 in the atomic ratio, respectively, to 1.00 (atomic
ratio) of the combination of La 80% by weight and Pr 20% by weight
(the combination with 20% of La substituted by Pr). They were
combined and melted in a high-frequency melting furnace. Then, they
were cooled to yield the alloy of the LaNi.sub.5 group.
[0041] The obtained alloy was subjected to a heat treatment in an
Ar atmosphere at 900.degree. C. for 5 hours, and pulverized so as
to produce hydrogen absorbing alloy powder with the average
particle diameter of 40 .mu.m. And 0.3 weight parts of
Yb.sub.2O.sub.3 (Ex.1) or Er.sub.2O.sub.3 (Ex.2) was added to 100
weight parts of the obtained alloy powder. After an addition of 100
ml water per 100 g of the alloy power, the resulting mixture was
wet-mixed for 30 minute, filtered, dried and finally, treated
thermally at the temperature of 250.degree. C. for 1 hour in a
vacuum. To 16 g of the obtained hydrogen absorbing alloy was added
4 g of aqueous 3% by weight PVA solution. Mixing them produced a
paste. A foamed porous body of nickel with porosity of 95% was
filled uniformly with the paste, and then pressed to yield a sheet
with a thickness of 0.5 to 1.0 mm. The sheet was furnished with a
lead on the surface to obtain a negative electrode. A known foamed
metal type of nickel having a capacity of 2400 mAh was used as a
positive electrode.
[0042] The obtained sheet of the negative electrode was wrapped to
the positive electrode through a separator formed of a
polypropylene nonwoven fabric which had been subjected to a known
hydrophilic treatment. The wrapped electrodes were placed in a
cylindrical vessel, where an electrolytic solution of aqueous 6N
KOH solution was added. Then, the vessel was sealed to yield a
SC-sized and sealed nickel-hydrogen storage battery. The obtained
battery was subjected at the constant temperature of 20.degree. C.
to the cycle of charge at 720 mA for 4 hours and discharge at 720
mA until the battery voltage became 1.0 V. After this cycle was
repeated 10 times, the battery was charged at 720 mA at 20.degree.
C. and discharged at 2400 mA until the battery voltage became 1.0
V.
[0043] The "retention percentage (%)" of discharge capacity for 720
mA and 2400 mA was thus obtained as shown in Table 1. The
"retention percentage (%)" is a ratio of the discharge capacity at
2400 mA to the discharge capacity at 720 mA, being expressed in
percentage. Repeating cycles of charge at 720 mA at 4 hours and
discharge at 720 mA until the battery voltage being 1.0, the number
of the cycles at which the capacity reached 60% of the initial
capacity was recorded as "cycle life".
EXAMPLES 3 and 4
[0044] Ni, Co, Mn and Al each was weighed so as to be 3.70, 0.70.
0.30 and 0.30 in the atomic ratio, respectively, to 0.95 (atomic
ratio) of the combination of La 60% by weight and Pr 40% by weight
(the combination with 40% of La substituted by Pr). They were
combined, melted and went through the same procedure as described
in Example 1 to produce hydrogen absorbing alloy powder with the
average particle diameter of 40 .mu.m. After an addition of 0.5
weight parts of Gd.sub.2O.sub.3 (Ex.3) or Dy.sub.2O.sub.3 (Ex.4) to
100 weight parts of the obtained alloy powder and a dry-mixing, the
thermal treatment was carried out at 400.degree. C. in an Ar
atmosphere for 1 hour. To 16 g of the obtained hydrogen absorbing
alloy was added 4 g of aqueous 3% by weight PVA solution. Mixing
them produced a paste. A foamed porous body of nickel with porosity
of 95% was filled uniformly with the paste, and then pressed to
yield a sheet with a thickness of 0.5 to 1.0 mm. The sheet was
furnished with a lead on the surface to obtain a negative
electrode. The following procedure was same as described in Example
1.
EXAMPLES 5 and 6
[0045] Ni, Co, Mn and Al each was weighed so as to be 4.00, 0.50.
0.20 and 0.30 in the atomic ratio, respectively, to 1.02 (atomic
ratio) of the combination of La 70% by weight and Nd 30% by weight
(the combination with 30% of La substituted by Nd). They were
combined, melted and went through the same procedure as described
in Example 1 to produce hydrogen absorbing alloy powder with the
average particle diameter of 40 .mu.m. After an addition of 1.0
weight parts of Pr.sub.6O.sub.11 (Ex.5) or La.sub.2O.sub.3 (Ex.6)
to 100 weight parts of the obtained alloy powder and a dry-mixing,
the thermal treatment was carried at 500.degree. C. in an Ar
atmosphere for 1 hour. To 16 g of the obtained hydrogen absorbing
alloy was added 4 g of aqueous 3% by weight PVA solution. Mixing
them produced a paste. A foamed porous body of nickel with porosity
of 95% was filled uniformly with the paste, and then pressed to
yield a sheet with a thickness of 0.5 to 1.0 mm. The sheet was
furnished with a lead on the surface to obtain a negative
electrode. The following procedure was same as described in Example
1.
EXAMPLES 7 and 8
[0046] Ni, Co, Mn and Al each was weighed so as to be 3.80, 0.70.
0.40 and 0.30 in the atomic ratio, respectively, to 0.98 (atomic
ratio) of the combination of La 80% by weight and Ce 20% by weight
(the combination with 20% of La substituted by Pr). They were
combined, melted and went through the same procedure as described
in Example 1 to produce hydrogen absorbing alloy powder with the
average particle diameter of 40 .mu.m. After an addition of 1.0
weight parts of Yb.sub.2O.sub.3 (Ex.7) or Er.sub.2O.sub.3 (Ex.8) to
100 weight parts of the obtained alloy powder and a dry-mixing, the
thermal treatment was carried out at 400.degree. C. in an Ar
atmosphere for 1 hour. To 16 g of the obtained hydrogen absorbing
alloy was added 4 g of aqueous 3% by weight PVA solution. Mixing
them produced a paste. A foamed porous body of nickel with porosity
of 95% was filled uniformly with the paste, and then pressed to
yield a sheet with a thickness of 0.5 to 1.0 mm. The sheet was
furnished with a lead on the surface to obtain a negative
electrode. The following procedure was same as described in Example
1.
EXAMPLES 9 and 10
[0047] Ni, Co, Mn and Al each was weighed so as to be 3.80, 0.70.
0.40 and 0.30 in the atomic ratio, respectively, to 0.98 (atomic
ratio) of the combination of La 80% by weight and Ce 20% by weight
(the combination with 20% of La substituted by Pr). They were
combined, melted and went through the same procedure as described
in Example 1 to produce hydrogen absorbing alloy powder with the
average particle diameter of 40 .mu.m. After an addition of 0.5
weight parts of a mixture with 2:1 of a weight ratio of
Yb.sub.2O.sub.3 to MnO.sub.2 (Ex.9) or 0.5 weight parts of a
mixture with 2:1 of a weight ratio of Er.sub.2O.sub.3 to MnO.sub.2
(Ex.10), respectively to 100 weight parts of the obtained alloy
powder and a dry-mixing, the thermal treatment was carried out at
200.degree. C. in an Ar atmosphere containing 10% by weight of
H.sub.2O vapor (Ar:H.sub.2O=9:1) for 1 hour. To 16 g of the
obtained hydrogen absorbing alloy was added 4 g of aqueous 3% by
weight PVA solution. Mixing them produced a paste. A foamed porous
body of nickel with porosity of 95% was filled uniformly with the
paste, and then pressed to yield a sheet with a thickness of 0.5 to
1.0 mm. The sheet was furnished with a lead on the surface to
obtain a negative electrode. The following procedure was same as
described in Example 1.
EXAMPLES 11 and 12
[0048] Ni, Co, Mn and Al each was weighed so as to be 3.80, 0.70.
0.40 and 0.30 in the atomic ratio, respectively, to 0.98 (atomic
ratio) of the combination of La 80% by weight and Ce 20% by weight
(the combination with 20% of La substituted by Pr). They were
combined, melted and went through the same procedure as described
in Example 1 to produce hydrogen absorbing alloy powder with the
average particle diameter of 40 .mu.m. After an addition of 0.5
weight parts of a mixture with 2:1 of a weight ratio of
Yb.sub.2O.sub.3 to Pr.sub.6O.sub.11 (Ex.11) or 0.5 weight parts of
a mixture with 2:1 of a weight ratio of Y.sub.2O.sub.3 to
Nd.sub.2O.sub.3 (Ex.12), respectively to 100 weight parts of the
obtained alloy powder and a dry-mixing in an Ar atmosphere, the
thermal treatment was carried out at 400.degree. C. in an Ar
atmosphere containing 10% by weight of H.sub.2O vapor
(Ar:H.sub.2O=9:1) for 1 hour. To 16 g of the obtained hydrogen
absorbing alloy was added 4 g of aqueous 3% by weight PVA solution.
Mixing them produced a paste. A foamed porous body of nickel with
porosity of 95% was filled with the paste, and then pressed to
yield a sheet with a thickness of 0.5 to 1.0 mm. The sheet was
furnished with a lead on the surface to obtain a negative
electrode. The following procedure was same as described in Example
1.
EXAMPLES 13 to 16
[0049] Ni, Co, Mn and Al each was weighed so as to be 3.70, 0.70.
0.30 and 0.30 in the atomic ratio, respectively, to 0.98 (atomic
ratio) of the combination of La 60% by weight and Nd 40% by weight
(the combination with 40% of La substituted by Nd). They were
combined, melted and went through the same procedure as described
in Example 1 to produce hydrogen absorbing alloy powder with the
average particle diameter of 40 .mu.m. After an addition of 0.5
weight parts of Er(OH).sub.3 (Ex.13), Dy(OH).sub.3 (Ex.14),
La(OH).sub.3 (Ex.15) or Gd(OH).sub.3 (Ex.16) to 100 weights parts
of the obtained alloy powder and dry-mixing in an Ar atmosphere,
the thermal treatment was carried out at 400.degree. C. in an Ar
atmosphere for 1 hour. To 16 g of the obtained hydrogen absorbing
alloy was added 4 g of aqueous 3% by weight PVA solution. Mixing
them produced a paste. A foamed porous body of nickel with porosity
of 95% was filled with the paste, and then pressed to yield a sheet
with a thickness of 0.5 to 1.0 mm. The sheet was furnished with a
lead on the surface to obtain a negative electrode. The following
procedure was same as described in Example 1.
EXAMPLE 17
[0050] Ni, Co, Mn and Al each was weighed so as to be 3.80, 0.70.
0.40 and 0.30 in the atomic ratio, respectively, to 0.98 (atomic
ratio) of the combination of La 80% by weight and Ce 20% by weight
(the combination with 20% of La substituted by Ce). They were
combined, melted and went through the same procedure as described
in Example 1 to produce hydrogen absorbing alloy powder with the
average particle diameter of 40 .mu.m. After an addition of 0.5
weight parts of a mixture with 1:1 of a weight ratio of
Yb(OH).sub.3 to MnO.sub.2, to 100 weight parts of the obtained
alloy powder and a dry-mixing in an Ar atmosphere, the thermal
treatment was carried out at 350.degree. C. in an Ar atmosphere
containing 10% by weight of H.sub.2O vapor (Ar:H.sub.2O=9:1) for 1
hour. To 16 g of the obtained hydrogen absorbing alloy obtained was
added 4 g of aqueous 3% by weight PVA solution. Mixing them
produced a paste. A foamed porous body of nickel with porosity of
95% was filled with the paste, and then pressed to yield a sheet
with a thickness of 0.5 to 1.0 mm. The sheet was furnished with a
lead on the surface to obtain a negative electrode. The following
procedure was same as described in Example 1.
EXAMPLES 18 to 21
[0051] Ni, Co, Mn and Al each was weighed so as to be 3.70, 0.70.
0.30 and 0.30 in the atomic ratio, respectively, to 0.95 (atomic
ratio) of the combination of La 60% by weight and Pr 40% by weight
(the combination with 40% of La substituted by Pr). They were
combined, melted and went through the same procedure as described
in Example 1 to produce hydrogen absorbing alloy powder with the
average particle diameter of 40 .mu.m. After an addition of 0.2
weight parts (Ex.18), 5.0 weight parts (Ex.19), 15 weight parts
(Ex.20), 20 weight parts (Ex.21) or 25 weight parts (Ex.21) of
Yb.sub.2O.sub.3 to 100 weight parts of the obtained alloy powder
and a dry-mixing in an Ar atmosphere, the thermal treatment was
carried out at 350.degree. C. in an Ar atmosphere for 1 hour. To 16
g of the obtained hydrogen absorbing alloy was added 4 g of aqueous
3% by weight PVA solution. Mixing them produced a paste. A foamed
porous body of nickel with porosity of 95% was filled with the
paste, and then pressed to yield a sheet with a thickness of 0.5 to
1.0 mm. The sheet was furnished with a lead on the surface to
obtain a negative electrode. The following procedure was same as
described in Example 1.
Comparative Examples 1 to 4
[0052] The alloy of Example 1 was used and went through the same
procedure as Example 1, except the changed treatment conditions
shown in Table 1.
Surface Analyses
[0053] Surface analyses of the hydrogen absorbing powder obtained
in Examples 1 to 21 were carried out using AES (Auger electron
spectroscopy) and TEM (transmission electron microscope). The AES
analysis showed that islands of metal oxide or hydroxide and the
Ni-rich layer having a higher concentration of nickel than the
mother phase existed on the surface of the alloy. The TEM analysis
showed that the Co-rich layer having a higher concentration of
cobalt than the mother phase existed on the surface of the alloy.
The metal oxide and hydroxide were identified by X-ray powder
diffraction analysis.
1 TABLE 1 720 mA 2400 mA Added Discharge Discharge Retention
Amount* Treatment Capacity Capacity Percentage Cycle Additive (wt
%) Condition (mAh) (mAh) (%) Life Example 1 Yb.sub.2O.sub.3 0.3
vacuum 2400 1600 66.7 700 250.degree. C. Example 2 Er.sub.2O.sub.3
0.3 vacuum 2400 1700 70.8 715 250.degree. C. Example 3
Gd.sub.2O.sub.3 0.5 Ar 2400 1500 62.5 650 400.degree. C. Example 4
Dy.sub.2O.sub.3 0.5 Ar 2400 1500 62.5 700 400.degree. C. Example 5
Pr.sub.6O.sub.11 1.0 Ar 2400 1400 58.3 650 500.degree. C. Example 6
La.sub.2O.sub.3 1.0 Ar 2400 1400 58.3 600 500.degree. C. Example 7
Yb.sub.2O.sub.3 1.0 Ar 2400 1500 62.5 720 400.degree. C. Example 8
Er.sub.2O.sub.3 1.0 Ar 2400 1600 66.7 700 400.degree. C. Example 9
Yb.sub.2O.sub.3 0.5 Ar 2400 1500 62.5 650 MnO.sub.2 200.degree. C.
Example 10 Er.sub.2O.sub.3 0.5 Ar 2400 1500 62.5 650 MnO.sub.2
200.degree. C. Example 11 Y.sub.2O.sub.3 0.5 vacuum 2400 1400 58.3
700 Pr.sub.6O.sub.11 300.degree. C. Example 12 Y.sub.2O.sub.3 0.5
vacuum 2400 1400 58.3 650 Nd.sub.2O.sub.3 300.degree. C. Example 13
Er(OH).sub.3 0.5 Ar 2400 1500 62.5 650 400.degree. C. Example 14
Dy(OH).sub.3 0.5 Ar 2400 1500 62.5 620 400.degree. C. Example 15
La(OH).sub.3 0.5 Ar 2400 1400 58.3 600 400.degree. C. Example 16
Gd(OH).sub.3 0.5 Ar 2400 1600 66.7 650 400.degree. C. Example 17
Yb(OH).sub.3 0.5 Ar 2400 1500 62.5 700 MnO.sub.2 350.degree. C.
Example 18 Yb.sub.2O.sub.3 0.2 Ar 2400 1600 66.7 680 350.degree. C.
Example 19 Yb.sub.2O.sub.3 5.0 Ar 2400 1500 62.5 730 350.degree. C.
Example 20 Yb.sub.2O.sub.3 15.0 Ar 2400 1450 60.4 735 350.degree.
C. Example 21 Yb.sub.2O.sub.3 20.0 Ar 2400 1400 58.3 740
350.degree. C. Com. Ex. 1 -- -- untreated 2400 850 35.4 450 Com.
Ex. 2 Yb.sub.2O.sub.3 0.5 Ar 2400 1500 62.5 200 850.degree. C. Com.
Ex. 3 Yb.sub.2O.sub.3 0.5 Ar 2400 850 35.4 400 80.degree. C. Com.
Ex. 4 Yb.sub.2O.sub.3 1.0 untreated 2400 850 35.4 720 *"Added
amount (wt %)" is a weight % to the alloy.
* * * * *