U.S. patent application number 10/473292 was filed with the patent office on 2004-08-19 for hydrogen storage alloy, production method therefor and ickel-hydrogen secondary battery- use cathode.
Invention is credited to Ikeda, Hideaki, Takamaru, Kiyofumi, Tatsumi, Koji.
Application Number | 20040159377 10/473292 |
Document ID | / |
Family ID | 18957479 |
Filed Date | 2004-08-19 |
United States Patent
Application |
20040159377 |
Kind Code |
A1 |
Takamaru, Kiyofumi ; et
al. |
August 19, 2004 |
Hydrogen storage alloy, production method therefor and
ickel-hydrogen secondary battery- use cathode
Abstract
The present invention relates to hydrogen storage alloys,
methods for producing the same, and anodes produced with such
alloys for nickel-hydrogen rechargeable batteries. The alloys are
useful as electrode materials for nickel-hydrogen rechargeable
batteries, excellent, when used as anode materials, in corrosion
resistance or activity such as initial activity and high rate
discharge performance, of low cost compared to the conventional
alloys with a higher Co content, and recyclable. The alloys are of
a composition represented by the formula (1), and has a
substantially single phase structure, and the crystals thereof have
an average long axis diameter of 30 to 160 .mu.m, or not smaller
than 5 .mu.m and smaller than 30 .mu.m. The present anodes for
rechargeable batteries contain at least one of these hydrogen
storage alloys. RNi.sub.xCo.sub.yM.sub.z (1) (R: rare earth
elements etc., M: Mg, Al, etc., 3.7.ltoreq.x.ltoreq.5.3,
0.1.ltoreq.y.ltoreq.0.5, 0.1.ltoreq.z.ltoreq.1.0,
5.1.ltoreq.x+y+z.ltoreq- .5.5)
Inventors: |
Takamaru, Kiyofumi;
(Kobe-shi, JP) ; Ikeda, Hideaki; (Kakogawa-shi,
JP) ; Tatsumi, Koji; (Chigasaki-shi, JP) |
Correspondence
Address: |
DARBY & DARBY P.C.
P. O. BOX 5257
NEW YORK
NY
10150-5257
US
|
Family ID: |
18957479 |
Appl. No.: |
10/473292 |
Filed: |
March 5, 2004 |
PCT Filed: |
March 29, 2002 |
PCT NO: |
PCT/JP02/03163 |
Current U.S.
Class: |
148/513 ;
148/426; 420/900; 429/218.2 |
Current CPC
Class: |
Y10S 420/90 20130101;
H01M 4/385 20130101; H01M 4/383 20130101; Y02E 60/10 20130101 |
Class at
Publication: |
148/513 ;
429/218.2; 420/900; 148/426 |
International
Class: |
H01M 004/58 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 3, 2001 |
JP |
2001-104652 |
Claims
What is claimed is:
1. A hydrogen storage alloy of a composition represented by the
formula (1), wherein said alloy has a substantially single phase
structure, and crystals of said alloy has an average long axis
diameter of 30 to 160 .mu.m: RNi.sub.xCo.sub.yM.sub.z (1) wherein R
stands for one or a mixture of rare earth elements including
yttrium, M stands for Mg, Al, Mn, Fe, Cu, Zr, Ti, Mo, W, B, or
mixtures thereof, x satisfies 3.7.ltoreq.x.ltoreq.5.3, y satisfies
0.1.ltoreq.y.ltoreq.0.5, z satisfies 0.1.ltoreq.z.ltoreq.1.0, and
5.1.ltoreq.x+y+z.ltoreq.5.5.
2. A hydrogen storage alloy of a composition represented by the
formula (1), wherein said alloy has a substantially single phase
structure, and crystals of said alloy have an average long axis
diameter of not smaller than 5 .mu.m and smaller than 30 .mu.m.
3. The hydrogen storage alloy of claim 1 or 2, wherein said R in
the formula (1) is selected from the group consisting of La, Ce,
Pr, Nd, and mixtures thereof.
4. The hydrogen storage alloy of claim 3, wherein a composition of
said R in the formula (1) is 50 to 100 at % La, 0 to 50 at % Ce, 0
to 50 at % Pr, and 0 to 50 at % Nd.
5. The hydrogen storage alloy of claim 1, wherein said average long
axis diameter is 30 to 120 .mu.m.
6. The hydrogen storage alloy of claim 2, wherein said average long
axis diameter is 10 to 20 .mu.m.
7. A method for producing an alloy of claim 1 comprising the steps
of: (A) melting materials for an alloy of a composition represented
by the formula (1) to prepare an alloy melt; (B-1) cooling and
solidifying said alloy melt into alloy flakes having an average
thickness of 0.1 to 0.5 mm; and (C-1) heat-treating said alloy
flakes at 950 to 1100.degree. C. for 30 minutes to 10 hours.
8. A method for producing an alloy of claim 2 comprising the steps
of: (A) melting materials for an alloy of a composition represented
by the formula (1) to prepare an alloy melt; (B-2) cooling and
solidifying said alloy melt into alloy flakes having an average
thickness of 0.05 to 0.2 mm; and (C-2) heat-treating said alloy
flakes at 900 to 1000.degree. C. for 1 to 10 hours.
9. An anode for a nickel-hydrogen rechargeable battery comprising a
hydrogen storage alloy of claim 1 and an electrically conductive
material as anode materials.
10. An anode for a nickel-hydrogen rechargeable battery comprising
a hydrogen storage alloy of claim 1, a hydrogen storage alloy of
claim 2, and an electrically conductive material as anode
materials.
11. The anode for a nickel-hydrogen rechargeable battery of claim
10, wherein a ratio of said hydrogen storage alloy of claim 1 to
said hydrogen storage alloy of claim 2 existing in said anode
materials is 99:1 to 90:10.
Description
FIELD OF ART
[0001] The present invention relates to hydrogen storage alloys,
methods for producing the same, and anodes for nickel-hydrogen
rechargeable batteries, which alloys are useful as electrode
materials for nickel-hydrogen rechargeable batteries, and when used
as the electrode materials, exhibit particularly excellent cycle
life characteristics.
BACKGROUND ART
[0002] Metal oxide-hydrogen batteries with a hydrogen anode made of
a hydrogen storage alloy have recently been attracting attention
for their inherently high energy density, advantageous volume
efficiency, safe operability, and excellence in both performance
and reliability. In this type of batteries, AB.sub.5 type hydrogen
storage alloys are mainly used as the anode material. For improved
battery performance, the alloys are demanded to have various
properties, such as hydrogen storage capacity, equilibrium
pressure, corrosion resistance, and flatness of the plateau. Some
of these properties are conflicting with each other, so that
studies have been made for improving one property without
sacrificing the other, some with practical success.
[0003] For improving the corrosion resistance of hydrogen storage
alloys, which will contribute to improved battery cycle life,
addition of cobalt (Co) to the alloys has been observed to give
certain effects and put into practice. However, since Co is very
expensive, the addition thereof disadvantageously increases the
alloy cost. Thus studies have been made to retain the corrosion
resistance of an alloy even at a reduced Co content. Various
solutions have been attempted for this purpose, such as using other
additional elements with Co, increasing the ratio of the B-site
components mainly consisting of Ni to the A-site components mainly
consisting of rare earth elements, and the combination of
these.
[0004] In the above methods, retention of the corrosion resistance
at a reduced Co content is achieved. However, another problem
arises in the method of using other additional elements, that the
increased number of compositional elements of the alloy makes
recycling of the used batteries difficult, which increases the
costs for recycling. In the method of increasing the ratio of the
B-site components, homogenization of the alloy structure is
difficult, which causes sharpening of the plateau slope or
formation of two plateaus, leading to decrease in the capacity and
internal pressure characteristics of the batteries.
[0005] Thus development of hydrogen storage alloys is demanded in
which the above problems have been overcome, and which are easy to
recycle, low in cost, and excellent in corrosion resistance.
[0006] On the other hand, for improving the activity of hydrogen
storage alloys with expectation of improvement in battery activity,
attempts have been made to treat the alloy surface with acid or
alkali, or to increase the ratio of the A-site components. However,
the activity conflicts with the corrosion resistance, and thus
these methods for improving the activity simultaneously impair the
corrosion resistance.
[0007] In the art of metal hydride-hydrogen batteries, electrode
active materials that satisfy both of these conflicting properties
have been under development, and as the materials for the active
materials, a mixture of an alloy excellent in corrosion resistance
and an alloy excellent in activity, has been proposed for use.
However, the alloys excellent in different properties used in this
method are also different in their compositions or structures, or
obtained by totally different production methods. Thus, even though
the activity and the corrosion resistance are improved, the
capacity and the internal pressure characteristics of the batteries
are reduced, or the costs for recycling the batteries after use are
increased.
SUMMARY OF THE INVENTION
[0008] It is therefor an object of the present invention to provide
hydrogen storage alloys, methods for producing the same, and anodes
produced with such alloys for nickel-hydrogen rechargeable
batteries, which alloys are useful as electrode materials for
nickel-hydrogen rechargeable batteries, which are excellent, when
used as anode materials, in both corrosion resistance and activity
such as initial activity and high rate discharge performance, which
are of low cost compared to the conventional alloys with a higher
Co content, and which are recyclable.
[0009] It is another object of the present invention to provide
anodes for nickel-hydrogen rechargeable batteries in which the
activity such as initial activity and high rate discharge
performance is well balanced with the conflicting corrosion
resistance, simply by using two or more kinds of particular
hydrogen storage alloys of different crystal grain sizes.
[0010] In order to achieve these objects, the inventors of the
present invention have made intensive studies in the relationship
between the composition and structure of alloys and the corrosion
resistance. As a result of the studies, the inventors have found
out that the above objects may be achieved by limiting the B-site
components within a particular range, giving the alloy a single
phase structure, and making the grain sizes of the crystals
constituting the alloy structure fall within a particular range, as
well as by producing anodes using two or more kinds of hydrogen
storage alloys of different crystal grain sizes. The present
inventors have also made studies for methods for producing alloys
that achieve the above objects, to complete methods for
industrially producing such alloys.
[0011] According to the present invention, there is provided a
hydrogen storage alloy of a composition represented by the formula
(1), wherein said alloy has a substantially single phase structure,
and crystals of said alloy have an average long axis diameter of 30
to 160 .mu.m:
RNi.sub.xCo.sub.yM.sub.z (1)
[0012] wherein R stands for one or a mixture of rare earth elements
including yttrium, M stands for Mg, Al, Mn, Fe, Cu, Zr, Ti, Mo, W,
B, or mixtures thereof, x satisfies 3.7.ltoreq.x.ltoreq.5.3, y
satisfies 0.1.ltoreq.y.ltoreq.0.5, z satisfies
0.1.ltoreq.z.ltoreq.1.0, and 5.1.ltoreq.x+y+z.ltoreq.5.5 (referred
to as alloy (a) hereinbelow).
[0013] According to the present invention, there is also provided a
hydrogen storage alloy of a composition represented by the formula
(1), wherein said alloy has a substantially single phase structure,
and crystals of said alloy have an average long axis diameter of
not smaller than 5 .mu.m and smaller than 30 .mu.m (referred to as
alloy (b) hereinbelow).
[0014] According to the present invention, there is also provided a
method for producing alloy (a) comprising the steps of:
[0015] (A) melting materials for an alloy of a composition
represented by the formula (1) to prepare an alloy melt;
[0016] (B-1) cooling and solidifying said alloy melt into alloy
flakes having an average thickness of 0.1 to 0.5 mm; and
[0017] (C-1) heat-treating said alloy flakes at 950 to 1100.degree.
C. for 30 minutes to 10 hours.
[0018] According to the present invention, there is further
provided a method for producing alloy (b) comprising the steps
of:
[0019] (A) melting materials for an alloy of a composition
represented by the formula (1) to prepare an alloy melt;
[0020] (B-2) cooling and solidifying said alloy melt into alloy
flakes having an average thickness of 0.05 to 0.2 mm; and
[0021] (C-2) heat-treating said alloy flakes at 900 to 1000.degree.
C. for 1 to 10 hours.
[0022] According to the present invention, there is also provided
an anode for a nickel-hydrogen rechargeable battery comprising
alloy (a) and an electrically conductive material as anode
materials.
[0023] According to the present invention, there is further
provided an anode for a nickel-hydrogen rechargeable battery
comprising alloy (a), alloy (b), and an electrically conductive
material as anode materials.
PREFERRED EMBODIMENTS OF THE INVENTION
[0024] The present invention will now be explained in detail.
[0025] The alloys (a) and (b) of the present invention both have
the composition represented by the formula (1). In the formula (1),
R stands for one or a mixture of two or more of rare earth elements
including yttrium. R may preferably be one or more elements
selected from the group consisting mainly of La, Ce, Pr, and Nd for
achieving improved corrosion resistance, when, for example, the
alloy is used as an anode active material for a nickel-hydrogen
rechargeable battery. It is preferred to increase the La content in
the composition of R for preparing an active material of high
capacity. The La content is preferably not lower than 50%, more
preferably not lower than 55%, most preferably not lower than 65%,
by atomic percent. Accordingly, when R is one or more elements
selected from the group consisting mainly of La, Ce, Pr, and Nd, it
is preferred to suitably select the composition of R from 50 to 100
at % La, 0 to 50 at % Ce, 0 to 50 at % Pr, and 0 to 50 at % of
Nd.
[0026] In the formula (1), x and y denote the atomic ratios of Ni
and Co, respectively. x representing the Ni content satisfies
3.7.ltoreq.x.ltoreq.5.3. As to y, the Co content is preferably as
low as possible as long as the desired corrosion resistance is
achieved, since one of the objects of the present invention is to
reduce the alloy cost by reducing the Co content. With the Co
content y of over 0.5, the corrosion resistance is improved, while
the alloy cost is increased. With the Co content y of less than
0.1, the corrosion resistance is inevitably lowered. Thus y is
0.1.ltoreq.y.ltoreq.0.5, preferably 0.2.ltoreq.y.ltoreq.0.45.
[0027] In the formula (1) , M represents additional elements for
adjusting the hydrogen storage performance of the alloy, and stands
for one or more elements selected from the group consisting of Mg,
Al, Mn, Fe, Cu, Zr, Ti, Mo, W, and B. When the alloy contains too
large a number of additional elements, the inconveniences in
recycling the alloy outstrip the contribution of the additional
elements to the alloy characteristics. Thus the number of
additional elements is preferably 2 to 5, more preferably 2 to 3.
The content of M is denoted by z. With z of less than 0.1, the
effect of the addition of the elements M on the alloy
characteristics is too little, whereas even with z of over 1.0, no
further increase in the effect is achieved, so that z is
0.1.ltoreq.z.ltoreq.1.0, preferably 0.35.ltoreq.z.ltoreq.1.0.
[0028] In the alloy of the present invention, the value of x+y+z
representing the ratio of the B-site elements is important. This
value is one of the factors for improving the corrosion resistance
of the alloy. If this value is less than 5.1, the corrosion
resistance cannot be improved, whereas if more than 5.5, it is
quite difficult to give the alloy a single phase structure, and the
corrosion resistance is lowered. Thus x+y+z is
5.1.ltoreq.x+y+z.ltoreq.5.5, preferably
5.2.ltoreq.x+y+z.ltoreq.5.4.
[0029] The structure of the present alloy is of a substantially
single phase for achieving the desired corrosion resistance.
Whether an alloy is of a single phase structure or not may be
confirmed by X-ray diffraction or under an electron microscope.
Having a substantially single phase structure herein means that the
presence of other phases cannot be observed clearly by these
methods.
[0030] In the alloy (a) of the present invention, the average long
axis diameter of the crystal grains is 30 to 160 .mu.m, preferably
30 to 120 .mu.m, more preferably 70 to 100 .mu.m, and it is
particularly preferred that the crystal grains are of a uniform
size, for further improving the corrosion resistance. With the
average long axis diameter of less than 30 .mu.m, the desired
corrosion resistance is hard to be achieved, whereas with the
average long axis diameter of over 160 .mu.m, the activity required
as an anode active material for a rechargeable battery cannot be
obtained.
[0031] In the alloy (b) of the present invention, the average long
axis diameter of the crystal grains is not smaller than 5 .mu.m and
smaller than 30 .mu.m, preferably not smaller than 10 .mu.m and
smaller than 30 .mu.m, more preferably 10-20 .mu.m, and it is
particularly preferred that the crystal grains are of a uniform
size for improving the activity when used in combination with the
alloy (a) as anode active materials for a rechargeable battery.
With the average long axis diameter of smaller than 5 .mu.m, the
desired corrosion resistance is hard to be achieved, whereas with
the average long axis diameter of not smaller than 30 .mu.m, the
activity as an anode active material for a rechargeable battery is
hard to be improved in combination with the alloy (a).
[0032] The alloys of the present invention, when used for example
as electrode materials, maybe subjected to surface coating by
plating or with a high polymer, surface treatment with an acid or
alkali solution, or any conventional treatment, for the purpose of
further improving various properties before the alloys are
processed into electrodes.
[0033] The alloys of the present invention may be produced, for
example, by the methods of the present invention including the
steps of: (A) melting the materials for an alloy of the composition
represented by the formula (1) to prepare an alloy melt; (B-1) or
(B-2) cooling and solidifying the alloy melt into alloy flakes
having the particular average thickness; and (C-1) or (C-2)
heat-treating the alloy flakes under the particular conditions. The
melting step (A) may be performed in a conventional manner.
[0034] According to the methods of the present invention, the
average long axis diameter of the crystals of the resulting alloys
may be regulated by controlling the cooling rate in preparing the
alloy flakes, the thickness of the alloy flakes, and the like
factors. In general, the higher the cooling rate is, the smaller
the long axis diameter of the crystal grains is, and vice versa. In
the methods of the present invention, since the alloys in the form
of as-cast flakes do not have a single phase structure, the alloy
flakes are subsequently heat-treated under the particular
conditions for giving a single phase structure thereto. If the
cooling rate in the production of the alloy flakes is too low, a
secondary phase of crystals appear, which grow so coarse that the
alloy flakes cannot be made into a single phase structure in the
subsequent heat treatment, thus not being preferred. On the other
hand, if the cooling rate is too high, the crystals are made fine
and readily made into a single phase structure, but the thickness
of the alloy flakes is hard to be controlled within the particular
range, and the productivity is lowered, thus not being
preferred.
[0035] In view of the above, the cooling rate in producing the
alloy flakes in the methods of the present invention is usually in
the range of 10 to 3000.degree. C. per second, preferably 100 to
1000.degree. C. per second. The cooling rate may suitably be
selected from the above range so that the alloy flakes have the
particular thickness, taking the alloy composition and thickness of
the alloy flakes into consideration.
[0036] In the method for producing alloy (a) of the present
invention, if the alloy flakes are too thick, the radial
temperature variation in the alloy flakes is great, which results
in difficulty in generating crystals of a uniform size. Too thick
alloy flakes also provide enlarged reaction areas, which cause too
much growth of the crystals in the subsequent long-time heat
treatment. Thus, in step (B-1), the thickness of the alloy flakes
should be adjusted to 0.1 to 0.5 mm, preferably 0.2 to 0.3 mm. Such
alloy flakes may preferably be produced by single- or twin-roll
strip casting, centrifugal casting, or rotary disk casting.
[0037] On the other hand, in the method for producing alloy (b) of
the present invention, since the average long axis diameter of the
crystals of the alloy (b) is smaller than that of the alloy (a) ,
the thickness of the alloy flakes should be adjusted to 0.05 to 0.2
mm in step (B-2).
[0038] In step (C-1) of the method for producing the alloy (a), the
heat treatment for giving the alloy flakes a single phase structure
is performed at 950 to 1100.degree. C. for 30 minutes to 10 hours.
At lower than 950.degree. C., it takes too much time for the
crystals to grow to the predetermined crystal grain size, resulting
in dispersion in the crystal grain size. At higher than
1100.degree. C., a secondary phase is reprecipitated, and the alloy
of a single phase structure cannot be obtained.
[0039] In step (C-2) of the method for producing the alloy (b), the
heat treatment for giving the alloy flakes a single phase structure
is performed at 900 to 1000.degree. C. for 1 to 10 hours. At lower
than 900.degree. C., the single phase structure is hard to be given
to the alloy flakes, and it takes time for the crystals to grow to
the predetermined crystal grain size. At higher than 1000.degree.
C., the crystals may grow beyond the predetermined grain size, or
dispersion may occur in the crystal grain sizes.
[0040] The anode for a nickel-hydrogen rechargeable battery of the
present invention contains the alloy (a), alloy (b), or a mixture
of alloys (a) and (b), and an electrically conductive material, as
anode materials. The alloy (a), alloy (b), or a mixture of alloys
(a) and (b) acts as an anode active material in the rechargeable
battery. The anode of the present invention may optionally contain
other conventionally-used components, as long as the objects of the
present invention is achieved, and may contain, in particular,
other active materials.
[0041] The anode for a nickel-hydrogen rechargeable battery of the
present invention may be produced using alloy (a) and/or alloy (b)
as the essential components of the active material, which are mixed
with a binder, an electrical conductivity assisting agent, and the
like in a conventional manner, and molded into an anode. There is
no particular limitation imposed on the binder and the electrical
conductivity assisting agent, and those used conventionally may be
used here.
[0042] When the alloy (a) alone is used as the active material, the
resulting anode exhibits excellent corrosion resistance, whereas
when the alloy (b) alone is used as the active material, the
resulting anode exhibits excellent initial activity and load
characteristics. When the two alloys are used in combination, the
resulting anode is given the properties of the both. For preparing
an anode for a battery for general use having initial activity and
corrosion resistance both improved, the mixing ratio of the alloy
(a) to the alloy (b) is preferably within a range of 99:1 to 90:10
by weight. If the mixing ratio of the alloy (b) to the alloy (a) is
too low, the initial activity cannot be improved sufficiently,
whereas if the mixing ratio of the alloy (b) is too high, the
corrosion resistance cannot be improved sufficiently, thus not
being preferred. For preparing an anode for a high-output power
battery having high rate discharge performance and corrosion
resistance both improved, the mixing ratio of the alloy (a) to the
alloy (b) is preferably within a range of 90:10 to 50:50. If the
mixing ratio of the alloy (a) to the alloy (b) is too low, the
corrosion resistance cannot be improved sufficiently, whereas if
the mixing ratio of the alloy (a) is too high, the high rate
discharge performance cannot be improved sufficiently, thus not
being preferred.
[0043] With the particular composition, substantially single phase
structure, and controlled average long axis diameter of the
crystals, the hydrogen storage alloys of the present invention are
useful as electrode materials for nickel-hydrogen rechargeable
batteries. When used as anode materials, the present alloys exhibit
excellent activities, such as initial activity and high rate
discharge performance, and excellent corrosion resistance. The
present alloys are also low in cost compared to the conventional
alloys with a higher Co content, and are recyclable. By the methods
of the present invention, such hydrogen storage alloys are easily
produced in an industrial scale.
[0044] Since the anodes for nickel-hydrogen rechargeable batteries
of the present invention contain the hydrogen storage alloys of the
present invention as the active materials, the advantages of the
present alloys when used for anodes for rechargeable batteries
mentioned above, are achieved. Further, nickel-hydrogen
rechargeable batteries in which the activity, in particular, the
initial activity and the high rate discharge performance, is well
balanced with the conflicting corrosion resistance, may be provided
simply by employing two or more kinds of particular hydrogen
storage alloys having different crystal grain sizes.
EXAMPLES
[0045] The present invention will now be explained in more detail
with reference to Examples and Comparative Examples, but the
present invention is not limited thereto.
Examples 1-19 and Comparative Examples 1-3
[0046] Misch metal (abbreviated as Mm hereinbelow) manufactured by
Santoku Corporation (rare earth composition: 70 at % La, 22 at %
Ce, 2 at % Pr, and 6 at % Nd) Ni, Co, Mn, and Al were mixed at the
elemental ratio of 4.00:0.40:0.65:0.20, and subjected to high
frequency induction melting in an alumina crucible in an argon gas
atmosphere to prepare an alloy melt. The alloy melt was rapidly
cooled by single-roll strip casting to prepare alloy flakes of a
hydrogen storage alloy having the average thickness shown in Table
1. The obtained alloy flakes were heat-treated in an argon gas
atmosphere under the conditions shown in Table 1.
[0047] The resulting heat-treated hydrogen storage alloy was
subjected to observation of its alloy structure under a scanning
electron microscope, and X-ray diffraction to see whether the alloy
was substantially of a single phase structure. Further, from the
alloy structure observed under a scanning electron microscope, the
average long axis diameter of the crystal grains along the
longitudinal axis of the alloy flakes was determined. The results
are shown in Table 1.
[0048] Next, the heat-treated alloy was mechanically pulverized to
prepare hydrogen storage alloy powders having the average particle
size of not larger than 60 .mu.m. 1.2 g of the alloy powders were
mixed with 1 g of carbonyl nickel as an electrically conductive
material and 0.2 g of fluororesin powders as a binder, and formed
into fibers. The resulting fibers were wrapped with nickel mesh,
and pressure molded under the pressure of 2.8 ton/cm.sup.2 to
thereby prepare an anode for a nickel-hydrogen rechargeable
battery. The obtained anode was placed in 30% KOH, and subjected to
a charge-discharge text in a pressure vessel under 5 atm for
evaluation of the initial activity, high rate discharge
performance, and corrosion resistance.
[0049] The charge-discharge test was run for 10 cycles at the
discharge current of 0.2 C, and the ratio of the discharge capacity
on the 3rd cycle to the discharge capacity on the 10th cycle was
taken as the initial activity. The test was further run, and the
capacity upon discharge at 1 C on the 11th cycle was measured, and
the ratio of this value to the discharge capacity on the 10th cycle
was taken as the high rate discharge performance. The test was
further run at the discharge current of 0.2 C from the 12th cycle
on, and the ratio of the capacity maintained on the 600th cycle to
the discharge capacity at the 10th cycle was taken as the corrosion
resistance. The results are shown in Table 1.
1TABLE 1 Average Temperature Duration of Average Long Axis High
Rate For Heat Heat Thickness of Diameter of Initial Discharge
Corrosion Treatment Treatment Cast Pieces Single Phase/ Main Phase
Activity Performance Resistance (.degree. C.) (hrs) (mm) Secondary
Phase (.mu.m) (%) (%) (%) Example 1 950 0.5 0.230 Single phase 33
95.9 89.7 91.1 Example 2 950 1 0.250 Single phase 62 94.3 86.9 94.8
Example 3 950 6 0.225 Single phase 73 93.9 88.2 95.4 Example 4 950
10 0.396 Single phase 95 93.6 85.6 96.7 Example 5 1000 0.5 0.270
Single phase 52 95.6 87.0 95.7 Example 6 1000 1 0.220 Single phase
72 94.0 85.8 95.8 Example 7 1000 6 0.347 Single phase 87 93.6 85.9
96.5 Example 8 1000 10 0.356 Single phase 89 94.5 85.4 96.0 Example
9 1050 0.5 0.357 Single phase 106 93.4 85.7 96.1 Example 10 1050 1
0.192 Single phase 74 94.2 86.0 96.6 Example 11 1050 6 0.203 Single
phase 76 93.5 86.3 96.3 Example 12 1050 10 0.392 Single phase 138
92.8 84.8 94.1 Example 13 1100 0.5 0.180 Single phase 53 95.1 88.7
93.0 Example 14 1100 1 0.272 Single phase 82 93.8 86.4 95.7 Example
15 1100 6 0.400 Single phase 118 93.5 85.5 95.7 Example 16 1100 10
0.467 Single phase 152 92.3 84.3 92.0 Example 17 900 10 0.163
Single phase 13 98.3 93.7 83.6 Example 18 950 6 0.181 Single phase
17 97.4 91.3 85.1 Example 19 1000 1 0.066 Single phase 15 97.7 92.2
84.6 Comp. Ex 1 850 10 0.146 Secondary phase 7.8 97.6 89.3 78.9
appeared Comp. Ex. 2 1200 5 0.289 Secondary phase 147 92.4 83.2
80.2 appeared Comp. Ex. 3 1000 10 0.593 Single phase 179 91.8 82.9
83.5
Examples 20-24 and Comparative Examples 4 and 5
[0050] Hydrogen storage alloys were prepared in the same manner and
under the same conditions as in Example 7, and subjected to each
evaluation, except that the alloy compositions were as shown in
Table 2. The results are shown in Table 2.
2TABLE 2 Corrosion La/ Ce/ Pr/ Nd/ Single Phase/ Resistance Ni Co
Al Mn AB.sub.x TRE TRE TRE TRE Secondary Phase (%) Example 20 3.93
0.50 0.30 0.37 5.10 50 25 5 20 Single phase 95.2 Example 21 4.15
0.20 0.40 0.45 5.20 60 40 0 0 Single phase 96.0 Example 22 4.15
0.40 0.30 0.45 5.30 72 21 2 6 Single phase 96.8 Example 23 4.10
0.30 0.43 0.57 5.40 83 12 1 4 Single phase 95.9 Example 24 4.35
0.10 0.40 0.65 5.50 100 0 0 0 Single phase 95.1 Comp. Ex. 4 3.75
0.40 0.25 0.60 5.00 60 23 3 14 Single phase 89.3 Comp. Ex. 5 4.35
0.30 0.50 0.45 5.60 82 10 2 6 Secondary phase 86.8 appeared
Examples 25-33 and Comparative Examples 6-9
[0051] The hydrogen storage alloy prepared in Example 7 (referred
to as alloy (a-1) hereinbelow) and the hydrogen storage alloy
prepared in Example 18 (referred to as alloy (b-1) hereinbelow)
were mixed at the mixing ratio shown in Table 3, and an anode for a
nickel-hydrogen rechargeable battery was produced in the same
manner as in Examples 1-19. The resulting anode was subjected to
each evaluation in the same manner as in Examples 1-19. The results
are shown in Table 3.
Comparative Example 10
[0052] A highly active alloy (c) having an equilibrium pressure 0.3
Mpa higher than that of alloy (a-1), was prepared through the
melting, casting, and heat-treating steps in the same manner as in
Example 7, except that the elemental ratio of the alloy was
Mm:Ni:Co:Al:Mn=1:3.55:0.- 80:0.25:0.37 (Rare earth (Mm)
composition: 41 wt % La, 43 wt % Ce, 4 wt % Pr, and 12 wt % Nd).
The alloy (a-1) and alloy (c) were mixed at the mixing ratio of.
50:50, and an anode for a nickel-hydrogen rechargeable battery was
produced in the same manner as in Examples 1-19. The resulting
anode was subjected to each evaluation in the same manner as in
Examples 1-19. The results are shown in Table 3.
3TABLE 3 High Rate Initial Discharge Corrosion Alloy Alloy Alloy
Activity Performance Resistance (a-1) (b-1) (c) (%) (%) (%) Example
25 99 1 0 95.8 90.2 96.3 Example 26 95 5 0 96.4 90.8 96.2 Example
27 90 10 0 97.1 91.2 96.0 Example 28 80 20 0 97.6 91.7 94.7 Example
29 70 30 0 98.0 92.0 94.0 Example 30 50 50 0 98.1 92.6 92.6 Comp.
Ex. 6 100 0 0 93.6 85.9 96.5 Comp. Ex. 7 40 60 0 98.1 92.9 91.3
Comp. Ex. 8 20 80 0 98.2 93.2 89.8 Comp. Ex. 9 0 100 0 98.3 93.7
83.6 Comp. Ex. 10 50 0 50 92.3 90.8 86.2
* * * * *