U.S. patent application number 13/587125 was filed with the patent office on 2012-12-20 for hydrogen storage alloy, hydrogen storage alloy electrode, secondary battery, and method for producing hydrogen storage alloy.
This patent application is currently assigned to National Institute of Advanced Science and Technology. Invention is credited to Tadashi KAKEYA, Manabu KANEMOTO, Minoru KUZUHARA, Tetsuya OZAKI, Tetsuo SAKAI, Masaharu WATADA.
Application Number | 20120318413 13/587125 |
Document ID | / |
Family ID | 39033024 |
Filed Date | 2012-12-20 |
United States Patent
Application |
20120318413 |
Kind Code |
A1 |
KAKEYA; Tadashi ; et
al. |
December 20, 2012 |
Hydrogen Storage Alloy, Hydrogen Storage Alloy Electrode, Secondary
Battery, And Method For Producing Hydrogen Storage Alloy
Abstract
Provided is a hydrogen storage alloy which is characterized in
that two or more crystal phases having different crystal structures
are layered in a c-axis direction of the crystal structures. The
hydrogen storage alloy is further characterized in that a
difference between a maximum value and a minimum value of a lattice
constant a in the crystal structures of the laminated two or more
crystal phases is 0.03 .ANG. or less.
Inventors: |
KAKEYA; Tadashi; (Kyoto,
JP) ; KANEMOTO; Manabu; (Kyoto, JP) ;
KUZUHARA; Minoru; (Kyoto, JP) ; OZAKI; Tetsuya;
(Kyoto, JP) ; WATADA; Masaharu; (Kyoto, JP)
; SAKAI; Tetsuo; (Osaka, JP) |
Assignee: |
National Institute of Advanced
Science and Technology
Tokyo
JP
GS Yuasa Corporation
Kyoto-shi
JP
|
Family ID: |
39033024 |
Appl. No.: |
13/587125 |
Filed: |
August 16, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12376922 |
Feb 9, 2009 |
|
|
|
PCT/JP2007/065507 |
Aug 8, 2007 |
|
|
|
13587125 |
|
|
|
|
Current U.S.
Class: |
148/555 ;
148/426; 148/429 |
Current CPC
Class: |
Y02E 60/10 20130101;
C22C 19/007 20130101; H01M 2004/027 20130101; C22C 19/03 20130101;
C22F 1/10 20130101; H01M 4/366 20130101; C22C 1/0441 20130101; H01M
10/345 20130101; C22C 1/023 20130101; Y10T 428/12493 20150115; H01M
4/134 20130101; C22F 1/002 20130101; H01M 4/1395 20130101; H01M
4/383 20130101 |
Class at
Publication: |
148/555 ;
148/429; 148/426 |
International
Class: |
C22C 19/03 20060101
C22C019/03; C22F 1/10 20060101 C22F001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2006 |
JP |
JP 2006-217488 |
Claims
1-4. (canceled)
5. A hydrogen storage alloy containing two or more crystal phases
having different crystal structures, wherein the two or more
crystal phases are layered in the c-axis direction of the crystal
structures and the hydrogen storage alloy has a composition defined
by a general formula R1.sub.dR2.sub.eR4.sub.fR5.sub.g (wherein R1
is one or more kind elements selected from the group consisting of
rare earth metals including Y; R2 is one or more kind elements
selected from the group consisting of Mg, Ca, Sr, and Ba; R4 is one
or more kind elements selected from the group consisting of Ni, Co,
Cr, Fe, Cu, Zn, Si, Sn, V, Nb, Ta, Ti, Zr, and Hf; R5 is one or two
elements selected from Mn and Al; and d, e, f, and g satisfy
8.ltoreq.d.ltoreq.19; 2.ltoreq.e.ltoreq.9; 73.ltoreq.f.ltoreq.79;
1.ltoreq.g.ltoreq.4; and d+e+f+g=100) and satisfies
3.53.ltoreq.(B/A).ltoreq.3.80 and
0.0593(B/A)+1.59.ltoreq.rA.ltoreq.0.0063(B/A)+1.81 in the case
(B/A) is defined as (f+g)/(d+e) and rA (.ANG.) is defined as the
average atomic radius of R1 and R2.
6. The hydrogen storage alloy according to claim 5, wherein the R1
is one or more kind elements R1' selected from the group consisting
of Ce, Pr, Nd, Sm, and Y and La at La/R1' ratio of 5 or less; R2 is
Mg; the R4 is one or two elements selected from Ni and Co; the R5
is Al; and the d, e, f, and g satisfy 16.ltoreq.d.ltoreq.19;
2.ltoreq.e.ltoreq.5;
73.ltoreq.f.ltoreq.78;and2.ltoreq.g.ltoreq.4.
7. The hydrogen storage alloy according to claim 5 having, as a
main produced phase, a crystal phase having Pr.sub.5Co.sub.19 type
crystal structure or a crystal phase having Ce.sub.5Co.sub.19 type
crystal structure.
8. A hydrogen storage alloy containing two or more crystal phases
having different crystal structures, wherein the two or more
crystal phases are layered in the c-axis direction of the crystal
structures and the hydrogen storage alloy has, as a main produced
phase, a crystal phase having Ce.sub.5Co.sub.19 type crystal
structure and a composition defined by a general formula
La.sub.hR6.sub.iR7.sub.jMg.sub.kR8.sub.m (wherein R6 is one or more
kind elements selected from the group consisting of rare earth
metals including Y and excluding La; R7 is one or more kind
elements selected from the group consisting of Zr, Ti, Zn, Sn and
V; R8 is one or more kind elements selected from the group
consisting of Ni, Co, Mn, Al, Cu, Fe, Cr, and Si; and h, j, k and m
satisfy 0.ltoreq.j.ltoreq.0.65; 2.ltoreq.k.ltoreq.5.5;
0.70.ltoreq.h/(h+i).ltoreq.0.85;and h+i+j+k+m=100).
9. A hydrogen storage alloy containing two or more crystal phases
having different crystal structures, wherein the two or more
crystal phases are layered in the c-axis direction of the crystal
structures and the ratio of the crystal phase having CaCu.sub.5
type crystal structure is 22% by weight or less.
10. The hydrogen storage alloy according to claim 9, wherein the
hydrogen equilibrium pressure is 0.07 MPa or less.
11. The hydrogen storage alloy according to claim 9 having a
composition defined by a general formula
R1.sub.nR2.sub.pR4.sub.qR5.sub.r (wherein R1 is one or more kind
elements selected from the group consisting of rare earth metals
including Y; R2 is one or more kind elements selected from the
group consisting of Mg, Ca, Sr, and Ba; R4 is one or more kind
elements selected from the group consisting of Ni, Co, Cr, Fe, Cu,
Zn, Si, Sn, V, Nb, Ta, Ti, Zr, and Hf; R5 is one or two kind
elements selected from Mn and Al; and n, p, q, and r satisfy
16.ltoreq.n.ltoreq.23; 2.ltoreq.p.ltoreq.8;
68.5.ltoreq.q.ltoreq.76; 1.ltoreq.r.ltoreq.6.5; and
n+p+q+=100).
12. The hydrogen storage alloy according to claim 9, wherein the
content of Mn is 5% by weight or less.
13-14. (canceled)
15. A method for producing a hydrogen storage alloy containing two
or more crystal phases having different crystal structures, wherein
the two or more crystal phases, are layered in the c-axis direction
of the structures the method comprising a melting step of heat
melting alloy raw materials at prescribed mixing ratio in inert gas
atmosphere; a cooling step of rapid solidification the melted
alloy; and an annealing step of further annealing the alloy
subjected to the cooling step at a temperature that ranges from
860.degree. C. to 1000.degree. C. in inert gas atmosphere in
pressurized state.
16. The method for producing the hydrogen storage alloy according
to claim 15, wherein in the annealing step a pressurizing condition
is at a gauge pressure that ranges from 0.2 MPa to 1.0 MPa.
Description
TECHNICAL FIELD
[0001] The invention relates to a hydrogen storage alloy, a
hydrogen storage alloy electrode, a secondary battery, and a method
for producing a hydrogen storage alloy.
BACKGROUND ART
[0002] A hydrogen storage alloy is an alloy capable of safely and
easily storing hydrogen as an energy source and has drawn an
attention as a new energy conversion and storage material and its
application fields are in a wide range, e.g., hydrogen storage and
transportation, heat storage and transportation, heat-mechanical
energy conversion, separation and purification of hydrogen,
isolation of hydrogen isotopes, batteries using hydrogen as active
materials, catalysts for synthetic chemical, temperature sensors,
and so forth.
[0003] For example, a nickel-metal hydride battery using a hydrogen
storage alloy as a negative electrode material has characteristics
such as (a) high capacity; (b) durability to overcharge and over
discharge; (c) capability of charging and discharging at high
efficiency; (d) cleanness and has been actively investigated to
have further improved capabilities (improvement of retention ratio
of capacity in the case of repeating charge and discharge, that is,
cycle life, improved capacity of the battery, etc.).
[0004] So far, an AB.sub.5 type rare earth-Ni-based alloy having a
CaCu.sub.5 type crystal structure has been put into practical use
as an electrode material for a nickel-metal hydride battery, one
application example of such a hydrogen storage alloy; however the
discharge capacity reaches almost a limit of about 300 mAh/g and
presently it becomes difficult to further improve the capacity.
[0005] Further, as a new hydrogen storage alloy, a rare earth
metal-Mg--Ni based alloy, for example, LaCaMgNi.sub.9 alloys
(Patent Document 1) having a PuNi.sub.3 type crystal structure have
drawn attention and it is reported that a discharge capacity
exceeding that of an AB.sub.5 type alloy can be obtained by using
these alloy for electrode materials.
[0006] It is also reported that in addition of the crystal phase
having the AB.sub.5 type crystal structure, electrode materials of
hydrogen storage alloys containing a crystal phase of AB.sub.2 type
crystal structure such as MgCu.sub.2 type or rare earth
metal-Mg--Ni type alloys containing, as a main phase, the crystal
phase having Ce.sub.2Ni.sub.7 type, CeNi.sub.3 type, or
Gd.sub.2Co.sub.7 type crystal structure have high hydrogen storage
capacities and show good hydrogen release characteristics (Patent
Document 2).
[0007] Furthermore, with respect to alloys having Ce.sub.5CO.sub.19
type crystal structure, it is reported that electrodes complexed
with rare earth-Ni alloy having a CaCu.sub.5 type crystal structure
are excellent in hydrogenation reaction speed (Patent Document
3).
[0008] Patent Document 1: Japanese Patent No. 3015885
[0009] Patent Document 2: Japanese Patent Application Laid-Open
(JP-A) No. 11-323469
[0010] Patent Document 3: Japanese Patent No. 3490871
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0011] However, in the above-mentioned conventional hydrogen
storage alloys, a problem that the hydrogen storage capacity is
decreased in the case where hydrogen storage and release are
repeated has not sufficiently been solved yet.
[0012] Further, with respect to the conventional hydrogen storage
alloys, there is another problem that when the hydrogen storage
alloys are made to be excellent in the cycle life to quickly
release the stored hydrogen, the stored hydrogen is gradually
released simply by leaving the hydrogen storage alloys as they
are.
[0013] In view of the above state of the art, one aim of the
invention is to provide a hydrogen storage alloy of which the
hydrogen storage capacity is hardly decreased even if hydrogen
storage and release are repeated, that is, a hydrogen storage alloy
excellent in the cycle life.
[0014] Another aim of the invention is to provide a hydrogen
storage alloy excellent in the cycle life and having high hydrogen
storage amount.
[0015] Further, another aim of the invention is to provide a
hydrogen storage alloy having little self-release of hydrogen while
maintaining the excellent cycle life.
Means for Solving the Problems
[0016] To solve the above-mentioned problems, the inventors of the
invention have made various investigations and accordingly have
found that a hydrogen storage alloy having a layered structure of a
plurality of crystal phases with different crystal structures such
as a crystal phase of Pr.sub.5Co.sub.19 type crystal structure, a
crystal phase of Ce.sub.2Ni.sub.7 type crystal structure, and the
like can exhibit remarkably excellent cycle life and the finding
now leads to completion of the invention.
[0017] That is, the invention provides the following hydrogen
storage alloy, a hydrogen storage alloy electrode containing the
hydrogen storage alloy, a secondary battery comprising the
electrode, and a method of producing the hydrogen storage
alloy.
[0018] (1) A hydrogen storage alloy containing two or more crystal
phases having different crystal structures which are layered in the
c-axis direction of the crystal structures.
[0019] (2) The hydrogen storage alloy according to the above
description (1) in which the difference of the maximum value and
the minimum value of the lattice constant a in the crystal
structures of the layered two or more crystal phases is 0.03 .ANG.
or less.
[0020] (3) The hydrogen storage alloy according to the above
description (1) or (2) in which the crystal phases include two or
more types selected from a group consisting of a crystal phase
having La.sub.5MgNi.sub.24 type crystal structure, a crystal phase
having Ce.sub.5Co.sub.19 type crystal structure, and a crystal
phase having Ce.sub.2Ni.sub.7 type crystal structure.
[0021] (4) The hydrogen storage alloy according to one of the above
descriptions (1) to (3) having a composition defined by a general
formula Ra1.sub.aR2.sub.bR3.sub.c (wherein R1 is one or more kind
elements selected from a group consisting of rare earth metals
including Y; R2 is one or more kind elements selected from a group
consisting of Mg, Ca, Sr, and Ba; R3 is one or more kind elements
selected from a group consisting of Ni, Co, Mn, Al, Cr, Fe, Cu, Zn,
Si, Sn, V, Nb, Ta, Ti, Zr, and Hf; and a, b, and c satisfy
10.ltoreq.a.ltoreq.30; 1.ltoreq.b .ltoreq.10;
65.ltoreq.c.ltoreq.90; and a+b+c=100).
[0022] (5) The hydrogen storage alloy according to the above
description (1) having a composition defined by a general formula
R1.sub.dR2.sub.eR4.sub.fR5.sub.g (wherein R1 is one or more kind
elements selected from a group consisting of rare earth metals
including Y; R2 is one or more kind elements selected from a group
consisting of Mg, Ca, Sr, and Ba; R4 is one or more kind elements
selected from a group consisting of Ni, Co, Cr, Fe, Cu, Zn, Si, Sn,
V, Nb, Ta, Zr, and Hf; R5 is one or two elements selected from Mn
and Al; and d, e, f, and g satisfy 8.ltoreq.d.ltoreq.19;
2.ltoreq.e.ltoreq.9; 73.ltoreq.f.ltoreq.79; 1.ltoreq.g.ltoreq.4;
and d+e+f+g=100) and satisfying 3.53.ltoreq.(B/A).ltoreq.3.80 and
0.0593(B/A)+1.59.ltoreq.rA.ltoreq.0.0063(B/A)+1.81 in the case
(B/A) is defined as (f+g)/(d+e) and rA (A) is defined as the
average atom radius of the R1 and R2.
[0023] (6) The hydrogen storage alloy according to the above
description (5) in which R1 consists of one or more kind elements
R1' selected from a group consisting of Ce, Pr, Nd, Sm, and Y and
La and the ratio of La/R1' is 5 or less; the R2 is Mg; the R4 is
one or two elements selected from Ni and Co; the R5 is Al; and d,
e, f, and g satisfy 16.ltoreq.d.ltoreq.19; 2.ltoreq.e.ltoreq.5;
73.ltoreq.f.ltoreq.78; and 2.ltoreq.g.ltoreq.4.
[0024] (7) The hydrogen storage alloy according to the above
description (5) or (6) having a main generative phase is a crystal
phase having Pr.sub.5Co.sub.19 type crystal structure or a crystal
phase having Ce.sub.5Co.sub.19 type crystal structure.
[0025] (8) The hydrogen storage alloy according to the above
description (1) having, as a main generative phase, a crystal phase
having Ce.sub.5Co.sub.19 type crystal structure and a composition
defined by a general formula
La.sub.hR6.sub.iR7.sub.jMg.sub.kR8.sub.m (wherein R6 is one or more
kind elements selected from a group consisting of rare earth metals
including Y and excluding La; R7 is one or more kind elements
selected from a group consisting of Zr, Ti, Zn, Sn and V; R8 is one
or more kind elements selected from a group consisting of Ni, Co,
Mn, Al, Cu, Fe, Cr, and Si; and h, i, j, k and m satisfy
0.ltoreq.j.ltoreq.0.65; 2.ltoreq.k.ltoreq.5.5;
0.70.ltoreq.h/(h+i).ltoreq.0.85; and h+i+j+k+m=100).
[0026] (9) The hydrogen storage alloy according to the above
description (1) in which the ratio of the crystal phase having
CaCu.sub.5 type crystal structure is 22% by weight or less.
[0027] (10) The hydrogen storage alloy according to the above
description (9) in which the hydrogen equilibrium pressure is 0.07
MPa or less.
[0028] (11) The hydrogen storage alloy according to the above
description (9) or (10) having a composition defined by a general
formula R1.sub.nR2.sub.pR4.sub.qR5.sub.r (wherein R1 is one or more
kind elements selected from a group consisting of rare earth metals
including Y; R2 is one or more kind elements selected from a group
consisting of Mg, Ca, Sr, and Ba; R4 is one or more kind elements
selected from a group consisting of Ni, Co, Cr, Fe, Cu, Zn, Si, Sn,
V, Nb, Ta, Ti, Zr, and Hf R5 is one or two kind elements selected
from Mn and Al; and n, p, q, and r satisfy 16.ltoreq.n.ltoreq.23;
2.ltoreq.p.ltoreq.8; 68.5.ltoreq.q.ltoreq.76;
1.ltoreq.r.ltoreq.6.5; and n+p+q+r=100).
[0029] (12) The hydrogen storage alloy according to one of the
above descriptions (9) to (11) wherein the content of Mn is 5% by
weight or less.
[0030] (13) A hydrogen storage alloy electrode using the hydrogen
storage alloy according to any one of the above descriptions (1) to
(12) as a hydrogen storage medium.
[0031] (14) A secondary battery using the hydrogen storage alloy
electrode according to the above description (13) as a negative
electrode.
[0032] (15) A method for producing the hydrogen storage alloy
according to one of the above descriptions (1) to (12), comprising
a melting step of heat melting alloy raw materials at prescribed
mixing ratio in inert gas atmosphere; a cooling step of rapid
solidification the melted alloy at a cooling speed of 1000.degree.
C./s or higher; and an annealing step of further annealing the
alloy subjected to the cooling step at 860.degree. C. or higher and
1000.degree. C. or lower in inert gas atmosphere in pressurized
state.
[0033] Herein, crystal phase in the invention means a region where
a single crystal structure exists.
Effect of the Invention
[0034] With respect to conventional hydrogen storage alloys, some
contain two or more crystal phases having crystal structures
different from one another. However, unlike the invention, these
crystal phases are not layered in the c-axis direction and exist
independently in individual regions. Therefore, it is supposed that
significant lattice strains are caused in the respective crystal
phases at the time of absorption and release of hydrogen are
repeated and as a result, deterioration of the alloys such as
pulverization is caused when absorption and release of hydrogen are
repeated, resulting in aggravation of the cycle life.
[0035] On the other hand, with respect to the hydrogen storage
alloy of the invention, two or more crystal phases having crystal
structures different from one another are layered in the c-axis
direction of the crystal structures. Therefore, the strains of the
crystal phases caused because of repeated absorption and release of
hydrogen are remarkably moderated. Such moderation of the strains
suppresses deterioration at the time of repeating absorption and
release of hydrogen and as a result, the cycle life can remarkably
be improved.
[0036] Accordingly, the hydrogen storage alloy of the invention is
provided with an effect to cause an excellent cycle life. Further,
since the hydrogen storage alloy electrode and the secondary
battery of the invention are configured by using such a hydrogen
storage alloy, even if discharge and charge are repeated, they are
provided with an excellent property that the discharge capacity is
hardly decreased. Furthermore, the method for producing the
hydrogen storage alloy of the invention is provided with an effect
to efficiently produce such a hydrogen storage alloy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1: A schematic drawing showing one embodiment of a
first hydrogen storage alloy.
[0038] FIG. 2: A TEM image showing one example of the first
hydrogen storage alloy.
[0039] FIG. 3: A magnified drawing of a portion of FIG. 2.
[0040] FIG. 4: A photograph showing the distribution of Ni and Mg
obtained by EPMA, with respect to Example 1 and Comparative Example
1.
[0041] FIG. 5: A graph showing the measurement results of cycle
life, with respect to hydrogen storage alloys of Example 1 and
Comparative Example 1.
[0042] FIG. 6: A graph showing a relation of the difference of the
a-axis length and the capacity retention ratio, with respect to the
hydrogen storage alloys of Examples 2 and 6.
[0043] FIG. 7: A graph formed by plotting the evaluation results of
the cycle life and discharge capacity using B/A and rA (A) as
coordinate axes, with respect to hydrogen storage alloys of
Examples 7 to 42.
[0044] FIG. 8: A graph showing the relation of the capacity
retention ratio to CaCu.sub.5 phase production ratio, with respect
to hydrogen storage alloys of Examples 82 to 91.
[0045] FIG. 9: A graph showing the relation of the remaining
discharge capacity to hydrogen equilibrium pressure, with respect
to hydrogen storage alloys of Examples 92 to 101.
[0046] FIG. 10: A graph formed by plotting the Ce content and the
cycle life, with respect to hydrogen storage alloys of Examples 102
to 109.
BEST MODES OF THE EMBODIMENTS
(First Hydrogen Storage Alloy)
[0047] The first hydrogen storage alloy of the invention contains
two or more crystal phases having crystal structures different from
one another and layered in the c-axis direction of the crystal
structures.
[0048] Examples of the above-mentioned crystal phases are a crystal
phase having a rhombohedral La.sub.5MgNi.sub.24 type crystal
structure (hereinafter, sometimes referred to simply
La.sub.5MgNi.sub.24 phase), a crystal phase having a hexagonal
Pr.sub.5Co.sub.19 type crystal structure (hereinafter, sometimes
referred to simply Pr.sub.5Co.sub.19 phase), a crystal phase having
a rhombohedral Ce.sub.5Co.sub.19 type crystal structure
(hereinafter, sometimes referred to simply Ce.sub.5Co.sub.19
phase), a crystal phase having a hexagonal Ce.sub.2Ni.sub.7 type
crystal structure (hereinafter, sometimes referred to simply
Ce.sub.2Ni.sub.7 phase), a crystal phase having a rhombohedral
Gd.sub.2Co.sub.7 type crystal structure (hereinafter, sometimes
referred to simply Gd.sub.2Co.sub.7 phase), a crystal phase having
a hexagonal CaCu.sub.5 type crystal structure (hereinafter,
sometimes referred to simply CaCu.sub.5 phase), a crystal phase
having a cubic AuBe.sub.5 type crystal structure (hereinafter,
sometimes referred to simply AuBe.sub.5 type phase), and a crystal
phase having a rhombohedral PuNi.sub.3 type crystal structure
(hereinafter, sometimes referred to simply PuNi.sub.3 phase).
[0049] Particularly, it is preferable to layer two or more kind
crystal phases selected from a group consisting of
La.sub.5MgNi.sub.24 phase, Pr.sub.5Co.sub.19 phase,
Ce.sub.5Co.sub.19 phase, and Ce.sub.2Ni.sub.7 phase. A hydrogen
storage alloy having layered structure of these crystal phases
cause less strains since the difference of the expansion and
shrinkage ratio among the respective crystal phases and thus has an
excellent property that less deterioration is caused at the time of
repeating hydrogen absorption and release.
[0050] Herein, the La.sub.5MgNi.sub.24 type crystal structure means
a crystal structure formed by inserting 4 AB.sub.5 units between
A.sub.2B.sub.4 units: the Pr.sub.5Co.sub.19 type crystal structure
means a crystal structure formed by inserting 3 AB.sub.5 units
between A.sub.2B.sub.4 units: the Ce.sub.5Co.sub.is type crystal
structure means a crystal structure formed by inserting 3 AB.sub.5
units between A.sub.2B.sub.4 units: the Ce.sub.2Ni.sub.7 type
crystal structure means a crystal structure formed by inserting 2
AB.sub.5 units between A.sub.2B.sub.4 units: the Gd.sub.2Co.sub.7
type crystal structure means a crystal structure formed by
inserting 2 AB.sub.5 units between A.sub.2B.sub.4 units: and the
AuBe.sub.5 type crystal structure means a crystal structure
composed of A.sub.2B.sub.4 units alone.
[0051] In addition, the A.sub.2B.sub.4 unit means a crystal lattice
having a hexagonal MgZn.sub.2 type crystal structure (C14
structure) or a hexagonal MgCu.sub.2 type crystal structure (C15
structure) and AB.sub.5 unit means a crystal lattice having a
hexagonal CaCu.sub.5 type crystal structure.
[0052] Further, A denotes any element selected from a group
consisting of rare earth metal elements and Mg and B denotes any
element selected from a group consisting of transition metal
elements and A1.
[0053] The layering order of the above-mentioned respective crystal
phases is not particularly limited and any specified crystal phase
combination may be layered repeatedly with periodicity or the
respective crystal phases may be layered at random without
periodicity.
[0054] In addition, with respect to the crystal phases having the
above-mentioned respective crystal structures, the crystal
structures can be specified by carrying out X-ray diffraction for
milled alloy powders and analyzing the obtained X-ray diffraction
patterns by Rietveld method.
[0055] A schematic drawing of one embodiment of the first hydrogen
storage alloy is shown in FIG. 1. As shown in FIG. 1, one
embodiment of the first hydrogen storage alloy is configured by
layering the CaCu.sub.5 phase, two Pr.sub.5Co.sub.19 phases
neighboring to the CaCu.sub.5 phase, and two Ce.sub.2Ni.sub.7 phase
neighboring to the Pr.sub.5Co.sub.19 phases in the c-axis direction
of the crystal structure.
[0056] Observation of the lattice image of the alloy by TEM makes
it possible to confirm the fact that two or more crystal phases
having different crystal structures are layered in the c-axis
direction of the crystal structures One example of the lattice
image of the first hydrogen storage alloy of the invention is shown
in FIG. 2 and FIG. 3.
[0057] These drawings shows that this hydrogen storage alloy is
configured by layering a crystal phase formed by repeating
arrangement of 3 AB.sub.5 units inserted between A.sub.2B.sub.4
units and a crystal phase formed by repeating arrangement of 4
AB.sub.5 units inserted between A.sub.2B.sub.4 units in the c-axis
direction. The former crystal phase is a crystal phase having the
Ce.sub.5Co.sub.19 phase crystal structure and the latter is a
crystal phase having the LaMgNi.sub.24 type crystal structure.
Observation of the lattice image by TEM in such a manner makes it
possible to confirm the fact that two or more crystal phases having
different crystal structures are layered in the c-axis direction,
which is a constituent factor of the invention.
[0058] As described, since the first hydrogen storage alloy of the
invention comprises two or more crystal phases having different
crystal structures and layered in the c-axis direction, the strains
of the crystal phases at the time of absorbing hydrogen can be
moderated by neighboring other crystal phases. Accordingly, even if
hydrogen absorption and release are repeated, less pulverization of
the alloy is caused and thus an excellent cycle life can be
caused.
(Second Hydrogen Storage Alloy)
[0059] The second hydrogen storage alloy of the invention is
configured by adjusting the difference of the maximum value and the
minimum value of the lattice constant a (hereinafter, also referred
to as a-axis length) in the crystal structures of the layered two
or more crystal phases to be 0.03 .ANG. or less in the first
hydrogen storage alloy.
[0060] When the difference of the maximum value and the minimum
value of the a-axis length of the respective crystal phases is
configured by adjusted to be 0.03 .ANG. or less, the strains among
the respective crystal phases caused at the time of hydrogen
absorption and release are further reduced and the hydrogen storage
alloy becomes difficult to be pulverized even if hydrogen
absorption and release are repeated, that is, the hydrogen storage
alloy becomes excellent in the cycle life.
[0061] The difference of the maximum value and the minimum value of
the a-axis length of the respective crystal phases is preferably
0.02 .ANG. or less, more preferably 0.016 .ANG. or less, and even
more preferably 0.01 .ANG. or less.
[0062] When the difference of the maximum value and the minimum
value of the a-axis length is in the above-mentioned range, the
capacity retention ratio of the hydrogen storage alloy is further
improved and the cycle life can be improved.
[0063] Herein, the a-axis length in the invention can be measured
by carrying out crystal structure analysis of the hydrogen storage
alloy by an X-ray diffraction apparatus. More practically, the
a-axis length can be calculated for each crystal phase by
determining the lattice constant of each crystal phase from XRD
patterns by Rietveld method (analysis software: RIETAN2000).
[0064] The above-mentioned first or second hydrogen storage alloy
is preferable to have a composition defined by a general formula
R1.sub.aR2.sub.bR3.sub.c (wherein R1 is one or more kind elements
selected from a group consisting of rare earth metals including Y;
R2 is one or more kind elements selected from a group consisting of
Mg, Ca, Sr, and Ba; R3 is one or more kind elements selected from a
group consisting of Ni, Co, Mn, Al, Cr, Fe, Cu, Zn, Si, Sn, V, Nb,
Ta, Ti, Zr, and Hf; and a, b, and c satisfy 10.ltoreq.a.ltoreq.30;
1.ltoreq.b.ltoreq.10; 65.ltoreq.c.ltoreq.90; and a+b+c=100).
(Third Hydrogen Storage Alloy)
[0065] The third hydrogen storage alloy of the invention is the
first hydrogen storage alloy further having a composition defined
by a general formula R1.sub.dR2.sub.eR4.sub.fR5.sub.g (wherein R1
is one or more kind elements selected from a group consisting of
rare earth metals including Y; R2 is one or more kind elements
selected from a group consisting of Mg, Ca, Sr, and Ba; R4 is one
or more kind elements selected from a group consisting of Ni, Co,
Cr, Fe, Cu, Zn, Si, Sn, V, Nb, Ta, Ti, Zr, and Hf; R5 is one or two
elements selected from Mn and Al; and d, e, f, and g satisfy
8.ltoreq.d.ltoreq.19; 2.ltoreq.e.ltoreq.9; 73.ltoreq.f.ltoreq.79;
1.ltoreq.g.ltoreq.4; and d+e+f+g=100) and satisfying
3.53.ltoreq.(B/A).ltoreq.3.80 and
0.0593(B/A)+1.59.ltoreq.rA.ltoreq.0.0063(B/A)+1.81, preferably
0.0593(B/A)+1.59.ltoreq.rA.ltoreq.1.827, in the case (B/A) is
defined as (f+g)/(d+e) and rA (.ANG.) is defined as the average
atomic radius of R1 and R2.
[0066] In the case the average atom radius rA (.ANG.) of the R1 and
R2 elements (that is, the element in the A side) composing the
crystal structures of the hydrogen storage alloy and the ratio
(B/A) of the R1 and R2 elements (that is, the elements in the A
side) to the R4 and R5 elements (that is, the elements in the B
side) satisfy the following relational expressions:
3.53.ltoreq.(B/A).ltoreq.3.80 and
0.0593(B/A)+1.59.ltoreq.rA.ltoreq.0.0063(B/A)+1.81: the R2 element
tends to be included in the A.sub.2B.sub.4 units and as a result,
segregation of the R2 element is prevented and it becomes easy to
form the layered body of the crystal phases having desired crystal
structures and accordingly, a hydrogen storage alloy excellent in
the cycle life can be obtained.
[0067] The third hydrogen storage alloy, preferably, wherein the R1
consists of one or more kind elements R1' selected from a group
consisting of Ce, Pr, Nd, Sm, and Y and La at La/R1' ratio or 5 or
less; the R2 is Mg; R4 is one or two elements selected from Ni and
Co; R5 is Al.
[0068] In the case where La is substituted with one or more kind
elements R1' selected from a group consisting of Ce, Pr, Nd, Sm,
and Y whose atomic radius are smaller than the La at La/R1' ratio
or 5 or less, and the R2 is Mg, the R4 is one or two elements
selected from Ni and Co, the R5 is A1, and the d, e, f, and g
respectively satisfy 16.ltoreq.d.ltoreq.19, 2.ltoreq.e.ltoreq.5,
73.ltoreq.f.ltoreq.78, and 2.ltoreq.g.ltoreq.4; Mg as the R2
element tends to be included further easier in the A.sub.2B.sub.4
units and accordingly, a hydrogen storage alloy excellent in the
cycle life can be obtained.
[0069] Third hydrogen storage alloy preferably contains a crystal
phase having Pr.sub.5Co.sub.19 type crystal structure or a crystal
phase having Ce.sub.5Co.sub.19 type crystal structure and further
preferably contains the crystal phase as the main produced
phase.
[0070] When the crystal phase having Pr.sub.5Co.sub.19 type crystal
structure or the crystal phase having Ce.sub.5Co.sub.19 type
crystal structure is the main produced phase, the lattice expansion
coefficient is small at the time of hydrogen absorption and
resulted in an action that less strains are caused, thereby giving
an effect to further improve the cycle life.
[0071] Herein, the main produced phase means the phase at the
highest production ratio.
(Fourth Hydrogen Storage Alloy)
[0072] The fourth hydrogen storage alloy of the invention is
configured to have, in the said first hydrogen storage alloy, a
crystal phase having Ce.sub.5Co.sub.19 type crystal structure and a
composition defined by a general formula
La.sub.hR6.sub.iR7.sub.jMg.sub.kR8.sub.m (wherein R6 is one or more
kind elements selected from a group consisting of rare earth metals
including Y and excluding La; R7 is one or more kind elements
selected from a group consisting of Zr, Ti, Zn, Sn and V; R8 is one
or more kind elements selected from a group consisting of Ni, Co,
Mn, Al, Cu, Fe, Cr, and Si; and h, i, j, k and m satisfy
0.70.ltoreq.h/(h+i).ltoreq.0.85; and h+i+j+k+m=100).
[0073] According to the fourth hydrogen storage alloy, since the
crystal phase having Ce.sub.5Co.sub.19 type crystal structure is
contained as an indispensable phase, the alloy becomes excellent in
the cycle life and furthermore, since the ratio h/(h+i) of La to
the total of La and R6 element is in a range satisfying
0.70.ltoreq.h/(h+i).ltoreq.0.85, segregation of Mg can be prevented
and the production ratio of the crystal phase having the CaCu.sub.5
type crystal structure which is inferior in the cycle life can be
decreased and on the other hand, the ratio of the crystal phase
having the Ce.sub.5Co.sub.19 type crystal structure which is
excellent in the cycle life is increased and as a result, a
hydrogen storage alloy having high hydrogen storage capacity and
excellent in the cycle life can be obtained.
[0074] In the fourth hydrogen storage alloy, j is preferable to be
0 or higher and 0.65 or lower and more preferable to be 0.2 or
higher and 0.65 or lower. When j is in the above-mentioned numeral
range, because of the existence of the R7 element (that is, one or
more kind elements selected from a group consisting of Zr, Ti, Zn,
Sn and V), Mg becomes diff cult to segregate and the ratio of the
crystal phase having the Ce.sub.5Co.sub.19 type crystal structure
is increased and the hydrogen storage capacity is increased.
[0075] Further, in the fourth hydrogen storage alloy, k is
preferable to be 2 or higher and 5.5 or lower and more preferable
to be 3 or higher and 5 or lower. When k is in the above-mentioned
numeral range, segregation of Mg is prevented and the hydrogen
storage alloy is provided with high hydrogen storage capacity and
becomes excellent in the cycle life.
(Fifth Hydrogen Storage Alloy)
[0076] The fifth hydrogen storage alloy of the invention is the
hydrogen storage alloy which contains 22% by weight or less of the
crystal phase having the CaCu.sub.5 type crystal structure
according to the first hydrogen storage alloy.
[0077] Conventionally, it is known that the crystal phase having
the CaCu.sub.5 type crystal structure is excellent in the cycle
life despite of a low discharge capacity. However, according to the
results of the investigations which the inventors of the invention
have made, it is found that in a hydrogen storage alloy configured
by layering two or more layers of crystal phases having crystal
structures different from one another, if the CaCu.sub.5 phase
exists much, the cycle life contrarily becomes difficult to be
improved.
[0078] The fifth hydrogen storage alloy is made further excellent
in the cycle life by adjusting the CaCu.sub.5 phase ratio to be 22%
by weight or less.
[0079] Further, in the fifth hydrogen storage alloy, the hydrogen
equilibrium pressure is 0.07 MPa or lower.
[0080] Conventionally, a hydrogen storage alloy has a property that
hydrogen absorption is difficult and release of absorbed hydrogen
is easy in the case of high hydrogen equilibrium pressure.
Accordingly, if the high rate capability is improved for the
hydrogen storage alloy, self-release of hydrogen becomes easy,
[0081] However, as a result of the investigations by the inventors,
it is found that a good high rate capability can be obtained in the
case where the hydrogen equilibrium pressure is set to be as low as
0.07 MPa or lower in the hydrogen storage alloy comprising two or
more layers of crystal phases having crystal structures different
from one another and containing 22% by weight or less of the
crystal phase having the CaCu.sub.5 type crystal structure. This
seems due to improvement in diffusivity of hydrogen in the
alloy.
[0082] Accordingly, in the fifth hydrogen storage alloy, the high
rate capability is made excellent and self-release of hydrogen (in
the case of a battery, self discharge) becomes difficult by setting
the hydrogen equilibrium pressure to be 0.07 MPa or lower.
[0083] Herein, the hydrogen equilibrium pressure means the
equilibrium pressure at H/M=0.5 (equilibrium pressure in the case
the ratio of hydrogen atoms to metal atoms is 0.5) in the PCT curve
(pressure-composition isothermal line) at 80.degree. C.
[0084] With respect to the fifth hydrogen storage alloy, the Mn
content in the alloy is preferable to be 5% by weight or less. When
the Mn content is adjusted to be 5% by weight or less, while the
high rate capability is maintained, the self-release of hydrogen
can further be suppressed.
[0085] Further, the fifth hydrogen storage alloy is preferable to
have a composition defined by a general formula
R1.sub.nR2.sub.pR4.sub.qR5.sub.r (wherein R1 is one or more kind
elements selected from a group consisting of rare earth metals
including Y; R2 is one or more kind elements selected from a group
consisting of Mg, Ca, Sr, and Ba; R4 is one or more kind elements
selected from a group consisting of Ni, Co, Cr, Fe, Cu, Zn, Si, Sn,
V, Nb, Ta, Ti, Zr, and Hf R5 is one or two kind elements selected
from Mn and Al; and n, p, q, and r satisfy 16.ltoreq.n.ltoreq.23;
2.ltoreq.p.ltoreq.8; 68.5.ltoreq.q.ltoreq.76;
1.ltoreq.r.ltoreq.6.5; and n+p+q+r=100).
[0086] In terms of saving material cost, the hydrogen storage alloy
according to the invention, misch metals (including La, Ce, Nd, and
Pr) are preferable to be used as raw materials. Use of the misch
metals as raw materials, the use amounts of costly high purity
materials such as neodymium and praseodymium can be suppressed and
at the same time same effect as that in the case of using the high
purity materials can be caused.
[0087] In the case the misch metals are used as raw materials, the
cerium content in the hydrogen storage alloy of the invention is
preferable to be 2.2 mol % or less. When the cerium content is
adjusted to be 2.2 mol % or less, decrease of the cycle life can be
suppressed. The effect of suppressing the decrease of the cycle
life become significant when the cerium content is 1.3 mol % or
less. Particularly, when the cerium content is adjusted to be 0.9
mol % or less, the decrease of the cycle life can be suppressed to
an extremely low level.
[0088] Further, in the case where the above-mentioned misch metals
are used as raw materials, in the hydrogen storage alloy of the
invention, it is preferable that the total ratio of the
Pr.sub.5Co.sub.19 phase, Ce.sub.5Co.sub.19 phase, and
Ce.sub.2Ni.sub.7 phase is 95% by weight or higher. With such
configuration, an excellent cycle life is exhibited. Particularly,
in the case where the total ratio of these three phases is 98% by
weight or higher, the effect becomes furthermore significant. Such
an effect is supposedly attributed to the suppression of
pulverization owing to the uniform alloy structure.
[0089] Next, a method for producing a hydrogen storage alloy of the
invention will be described.
[0090] A method for producing the first hydrogen storage alloy
involves a melting step of melting alloy raw materials mixed at a
prescribed composition ratio, a cooling step of rapid
solidification the molten alloy raw materials at a cooling speed of
1000 K/s or higher, and an annealing step of annealing the cooled
alloy at temperature range of 860.degree. C. or higher and
1000.degree. C. or lower in inert gas atmosphere in pressurized
state.
[0091] Herein, in the case the composition ratio of the alloy raw
materials is defined by a general formula R1.sub.sR2.sub.bR3.sub.c
(wherein R1 is one or more kind elements selected from a group
consisting of rare earth metals including Y; R2 is one or more kind
elements selected from a group consisting of Mg, Ca, Sr, and Ba; R3
is one or more kind elements selected from a group consisting of
Ni, Co, Mn, Al, Cr, Fe, Cu, Zn, Si, Sn, V, Nb, Ta, Ti, Zr, and Hf),
s, b, and c satisfy 8.ltoreq.s.ltoreq.30; 1.ltoreq.b.ltoreq.10;
65.ltoreq.c.ltoreq.90; and s+b+c=100.
[0092] If the hydrogen storage alloy is produced by such a
production method, it is made possible to obtain the hydrogen
storage alloy having two or more layered crystal phases having
crystal structures different from one another.
[0093] To explain it more concretely, at first, based on the
chemical composition of the aimed hydrogen storage alloy,
prescribed amount of a raw material ingot (an alloy raw material)
is weighed.
[0094] In the melting step, the above-mentioned alloy raw material
is put in a crucible and heated at, for example, 1200.degree. C. or
higher and 16000.degree. C. or lower, to melt the alloy raw
material using a high frequency melting furnace in an inert gas
atmosphere or vacuum.
[0095] In the cooling step, the melted alloy raw material is cooled
and solidified. The cooling speed is preferably 1000 K/s or higher
(also referred to as quenching). Quenching at 1000 K/s or higher is
effective to make the alloy structure very fine and uniform.
Further, the cooling speed can be set in a range of 1,000,000 K/s
or lower.
[0096] As the cooling method, practically, a melt spinning method
at a cooling speed of 100,000 K/s or higher and a gas atomization
method at a cooling speed of about 10,000 K/s or higher can
preferably be employed.
[0097] In the annealing step, in the pressurized state in inert gas
atmosphere, heating at 860.degree. C. or higher and 1000.degree. C.
or lower may be carried out using, for example, an electric furnace
or the like. As the pressurizing condition, it is preferable to be
0.2 MPa (gauge pressure) or higher and 1.0 MPa (gauge pressure) or
lower. Further, the treatment time for the annealing step is
preferably 3 hours or longer and 50 hours or shorter.
[0098] Such an annealing step is effective to release strains of
crystal lattice and the hydrogen storage alloy subjected to the
annealing step finally becomes the hydrogen storage alloy
comprising two or more layered crystal phases having crystal
structures different from one another.
[0099] A method for producing the second hydrogen storage alloy is
the method for producing according to the first hydrogen storage
alloy in which the temperature condition of the annealing step is
adjusted to be 890.degree. C. or higher and 970.degree. C. or
lower.
[0100] Adjustment of the condition in such a manner makes diffusion
of atoms relatively easy, suppresses evaporation of Mg, Ca, Sr, and
Ba, easily uniformalizes the length of the a-axis in the respective
crystal phases, and gives the hydrogen storage alloy having the
difference of 0.03 .ANG. between the maximum value and the minimum
value.
[0101] In the method for producing the second hydrogen storage
alloy, the temperature condition in the annealing step is
preferable to be 900.degree. C. or higher and 940.degree. C. or
lower. Adjustment of the condition in such a manner is effective to
make the concentration distribution of respective constituent
elements uniform and make the difference of the a-axis length among
the produced phases further shorter.
[0102] A method for producing the third hydrogen storage alloy is
the method for producing according to the first hydrogen storage
alloy in which the ratio of R1 and R2 elements of the alloy raw
material and the ratio of R4 and R5 elements are adjusted and the
above-mentioned average atom radium rA (.ANG.) and the ratio (B/A)
are satisfied in the case of consideration of the atom radius of
the respective elements.
[0103] Further, in the method for producing the third hydrogen
storage alloy, the average atom radium rA a) and the ratio (B/A)
are preferable to satisfy 1.810.ltoreq.rA.ltoreq.1.825 and
3.60.ltoreq.(B/A).ltoreq.3.70.
[0104] Adjustment of the condition in such a manner is effective to
maintain the high capacity and at the same time to give further
improved cycle performance.
[0105] A method for producing the fourth hydrogen storage alloy is
the method for producing the first hydrogen storage alloy in which
the alloy raw material composition is adjusted to give the
composition of the fourth hydrogen storage alloy and the
temperature condition in the annealing step is adjusted to be
890.degree. C. or higher and 970.degree. C. or lower.
[0106] Adjustment of the condition in such a manner makes diffusion
of atom relatively easy and effective to suppress evaporation of
Mg, Ca, Sr, and Ba, satisfy the prescribed composition, and obtain
the hydrogen storage alloy containing the crystal phase having the
Ce.sub.5Co.sub.19 type crystal structure.
[0107] Further, in the method for producing the fourth hydrogen
storage alloy, it is more preferable that in the above-mentioned
composition La.sub.hR6.sub.iR7.sub.jMg.sub.kR8.sub.m, k satisfies
3.4<k<4.3; R7 consists of one or more kind elements R7'
selected from a group consisting of Zr, Zn, and Sn in combination
with Ti and is defined as R7=Ti.sub.tR7'.sub.j-t (wherein
0.ltoreq.t<0.3); and R8 consists of one or more kind elements
R8' selected from a group consisting of Ni, Co, Cu, Fe, and Cr in
combination with Mn and defined as R8=Mn.sub.sR8'.sub.m-s (wherein
0<s<1.1).
[0108] Adjustment of the condition in such a manner is effective to
maintain the high capacity and at the same time to further improve
the cycle performance.
[0109] The method for producing the fifth hydrogen storage alloy is
the method for producing according to the first hydrogen storage
alloy in which the temperature condition in the annealing step is
adjusted to be 890.degree. C. or higher and 970.degree. C. or
lower.
[0110] Adjustment of the condition in such a manner makes diffusion
of atom relatively easy and effective to suppress evaporation of
Mg, Ca, Sr, and Ba, satisfy the prescribed composition, and obtain
the hydrogen storage alloy containing 20% by weight or less of the
crystal phase having the CaCu.sub.5 type crystal structure.
[0111] In the method for producing the fifth hydrogen storage
alloy, it is more preferable that in the composition
La.sub.uR9.sub.vMg.sub.wR10.sub.xR11.sub.y (wherein, R9 is at least
one element of Pr and Nd; R10 is at least one element of Ni and Co;
R11 is at least one element of Al and Mn; and u, v, w, x, and y
satisfy 4.255.ltoreq.u.ltoreq.17.39; 0.ltoreq.v.ltoreq.13.62;
2.128.ltoreq.w.ltoreq.4.701; 72.30.ltoreq.x.ltoreq.77.66; and
1.06.ltoreq.y.ltoreq.6.38).
[0112] Adjustment of the condition in such a manner is effective to
make Mg, Mn, and Al occupy specified atom sites in the layered
structure, stabilize their structure, and suppress production of
the crystal phase having the CaCu.sub.5 type crystal structure.
[0113] A hydrogen storage alloy electrode of the invention is
provided with the above-mentioned hydrogen storage alloy as a
hydrogen storage medium. At the time of using the hydrogen storage
alloy of the invention for an electrode as a heat storage medium,
it is preferable to pulverize the hydrogen storage alloy for the
use.
[0114] The pulverization of the hydrogen storage alloy at the time
of electrode production may be carried out either before or after
annealing, however, since the surface area becomes wide by the
pulverization, in terms of prevention of surface oxidation of the
alloy, it is desirable to pulverize the alloy after annealing. The
pulverization is preferable to carry out in inert atmosphere for
oxidation prevention of the alloy surface.
[0115] The pulverization may be carried out by, for example,
mechanical pulverization, hydrogenation pulverization, and the
like.
[0116] Further, a secondary battery of the invention is configured
to be a nickel-metal hydride battery using the hydrogen storage
alloy as a negative electrode. Since the hydrogen storage alloy of
the invention, that is the hydrogen storage alloy electrode, has
corrosion resistance to an aqueous strongly alkaline solution to be
used as an electrolytic solution of a nickel-metal hydride battery
or the like, it is excellent in the cycle performance in the case
where hydrogen absorption and release are repeatedly carried out.
As a result, the charge and discharge cycle performance of the
secondary battery also become excellent.
[0117] In addition, as a positive electrode of the secondary
battery, for example, nickel electrode (sintered type or
non-sintered type) is employed.
EXAMPLES
[0118] Hereinafter, the invention will be described more
practically, referring to Examples and Comparative Examples;
however the invention should not be limited to the following
Examples.
Example 1
[0119] A prescribed amount of a raw material ingot having the
chemical composition shown in Table 1 was weighed, put in a
crucible, and heated at 1500.degree. C. in reduced pressure argon
atmosphere using a high frequency melting furnace to melt the
material. After the melting, the melted alloy was quenched by
employing a melt spinning method and solidified.
[0120] Next, the obtained alloy was heated at 910.degree. C. in 0.2
MPa (gauge pressure, hereinafter the same) of pressurized argon
gas.
Comparative Example 1
[0121] A prescribed amount of a raw material ingot having the
chemical composition shown in Table 1 was weighed, put in a
crucible, and heated at 1500.degree. C. in reduced pressure argon
atmosphere using a high frequency melting furnace to melt the
material. After the melting, the melted alloy was quenched by
employing a melt spinning method and solidified.
[0122] Next, the obtained alloy was heated at 910.degree. C. in 0.2
MPa (gauge pressure, hereinafter the same) of pressurized argon
gas.
TABLE-US-00001 TABLE 1 La Pr Mg Ni Co Al Example 1 13.3 4.2 3.3
71.9 4.2 3.1 Comparative 12.8 4.3 4.3 68.1 6.4 4.3 Example 1
<Measurement of Crystal Structure and Calculation of Existence
Ratio>
[0123] Each obtained hydrogen storage alloy was pulverized to
obtain a powder with an average particle diameter (D50) of 20 .mu.m
and the powder was subjected to measurement under condition of 40
kV and 100 mA (Cu bulb) using an X-ray diffraction apparatus
(manufactured by Bruker AXS: model number M06XCE). Further, as
structure analysis, analysis by Rietveld method (analysis software:
RIETAN 2000) was carried and the production ratios of the produced
crystal phases in each hydrogen storage alloy were calculated.
[0124] The ratios (% by weight) of the produced phases are shown in
Table 2.
TABLE-US-00002 TABLE 2 Ce.sub.5Co.sub.19 Pr.sub.5Co.sub.19
CaCu.sub.5 AuBe.sub.5 phase phase phase phase Total Example 1 62.7
28.5 8.74 0.0 100 Comparative 69.1 16.1 11.8 3.0 100 example 1
<Evaluation of Distribution State of Crystal Phase>
[0125] With respect to the obtained hydrogen storage alloy powders
of Example and Comparative Example, the distribution state (color
map) of Ni and Mg was observed using EPMA (Electron Probe Micro
Analyzer) to evaluate the distribution state of produced phases.
With respect to Example 1 and Comparative Example 1, FIG. 4 shows
photographs of the distribution state (color map) of Ni and Mg
obtained by EPMA.
[0126] As shown in FIG. 4, it is observed that both Ni and Mg were
distributed uniformly in the hydrogen storage alloy of Example and
according to Rietveld analysis result or the like for the alloy, it
was confirmed that a plurality of phases were produced and as
comprehensive analysis of these results, it could be confirmed that
the crystal phases existed in layered state in the hydrogen storage
alloy. On the other hand, in the hydrogen storage alloy of
Comparative Example, Ni and Mg were distributed ununiformly in
places and thus it was supposed that the crystal phases separately
existed without forming a layered body. In addition, when the
lattice image of the hydrogen storage alloy of Example 1 was
observed by transmission electron microscope (TEM), the crystal
phases with the crystal structures different from one another were
layered in the c-axis direction.
<Evaluation of Cycle Performance>
(a) Production of Electrode
[0127] After 3 parts by weight of a nickel powder (manufactured by
INCO, #210) was added to 100 parts by weight of each of the
obtained hydrogen storage alloy powders of Example and Comparative
Example, an aqueous solution in which a thickener (methyl
cellulose) was dissolved was added and further 1.5 parts by weight
of a binder (styrene-butadiene rubber) was added to obtain a paste
which was applied to both faces of a punched steel plate (porosity
60%) with a thickness of 45 .mu.m and dried and thereafter pressed
in 0.36 mm thickness to obtain a negative electrode. On the other
hand, a sintered type nickel hydroxide electrode with an excess
capacity was used as a positive electrode.
(b) Production of Flooded Cell
[0128] The negative electrode produced in the above-mentioned
manner was sandwiched with positive electrodes while inserting
separators between them and these electrodes were fixed with bolts
at pressure of 1 kgf/cm.sup.2 to assemble an opened type cell. A
mixed solution of a 6.8 mol/L KOH solution and a 0.8 mol/L LiOH
solution was used as an electrolyte solution.
(c) Measurement Method of Discharge Capacity
[0129] In a water bath at 20.degree. C., charging and discharging
was repeated 65 cycles in condition of charging at 0.1 ItA to 150%,
discharging at 0.2 ItA to cut off voltage of -0.6 V (vs. Hg/HgO).
The results are shown in FIG. 5.
[0130] As shown in FIG. 5, with respect to the hydrogen storage
alloy of Comparative Example 1 in which the crystal phases existed
separately, the discharge capacity was lowered to about 88% after
the 65 cycles, whereas with respect to the hydrogen storage alloy
of Example 1, it was confirmed that the discharge capacity was
maintained at 99.7% even after 65 cycles.
Examples 2 to 6
[0131] Using the alloy materials with the compositions shown in the
following Table 3, hydrogen storage alloys of Examples 2 to 6 were
produced in the same manner as Example 1. When the lattice images
of these hydrogen storage alloys were observed by a transmission
electron microscope (TEM), it was confirmed that crystal phases
with different crystal structures were layered in the c-axis
direction.
TABLE-US-00003 TABLE 3 Unit: mol % La Pr Mg Ni Co Mn Al Example 2
12.58 4.19 4.19 71.28 2.10 2.10 2.10 Example 3 17.19 0.00 3.77
68.13 6.29 0.00 3.14 Example 4 9.64 8.18 3.14 75.89 0.00 0.00 1.68
Example 5 4.30 14.46 2.09 77.50 1.65 0.00 0.00 Example 6 5.01 14.08
2.12 74.50 4.29 0.00 0.00
<Measurement of A-Axis Length>
[0132] With respect to each of the obtained hydrogen storage
alloys, the production ratios of the crystal phases were calculated
and at the same time, the XRD patterns were measured by an X-ray
diffraction apparatus and the a-axis length for each produced
crystal phase was calculated by Rietveld method (analysis software:
RIETAN 2000). The results are shown in the following Table 4 and
FIG. 6.
[0133] Further, in the same manner as Example 1, the ratios of the
produced phases of each hydrogen storage alloy and the retention
ratio of the discharge capacity after 50 cycles were measured. The
results are also shown in Table 4.
TABLE-US-00004 TABLE 4 Ratios of produced crystal phase A-axis
Capacity (% by weight) [A-axis length (.ANG.)] length retention
Ce.sub.2Ni.sub.7 Ce.sub.5Co.sub.19 Pr.sub.5Co.sub.19 CaCu.sub.5
difference ratio phase phase phase phase (.ANG.) (%) Exam- 36.95
38.26 14.04 10.75 0.003 93.42 ple 2 [5.045] [5.044] [5.044] [5.043]
Exam- 26.43 35.11 20.42 18.04 0.016 92.87 ple 3 [5.066] [5.088]
[5.059] [5.050] Exam- 42.32 37.89 13.13 6.67 0.036 90.25 ple 4
[5.028] [5.017] [5.020] [4.992] Exam- 32.9 40.0 12.6 14.5 0.033
90.3 ple 5 [5.025] [5.015] [5.022] [4.992] Exam- 51.3 30.6 8.50
9.60 0.030 93.4 ple 6 [5.033] [5.029] [5.034] [5.004]
Examples 7 to 42
[0134] Using the alloy raw materials of the compositions shown in
the following Table 5, hydrogen storage alloys of Examples 7 to 42
were produced in the same manner as Example 1. When the lattice
images of these hydrogen storage alloys were observed by a
transmission electron microscope (TEM), it was confirmed that
crystal phases with different crystal structures were layered in
the c-axis direction.
Comparative Example 2
[0135] Similarly, using the allow raw material shown in Table 5, a
hydrogen storage alloy of Comparative Example 2 was produced in the
same manner as Comparative Example 1.
TABLE-US-00005 TABLE 5 Main Raw material composition produced rA La
Ce Pr Nd Sm Y Mg Ni Co Mn Al B/A phase .ANG. Example 7 12.4 0.0 4.1
0.0 0.0 0.0 4.1 71.1 4.1 1.0 3.1 3.85 Ce2Ni7 1.8122 Example 8 12.8
0.0 4.3 0.0 0.0 0.0 4.3 70.2 4.3 1.1 3.2 3.70 Pr5Co19 1.8122
Example 9 12.9 0.0 4.3 0.0 0.0 0.0 4.3 69.9 4.3 1.1 3.2 3.65
Pr5Co19 1.8122 Example 10 13.2 0.0 4.4 0.0 0.0 0.0 4.4 69.1 4.4 1.1
3.3 3.53 Pr5Co19 1.8122 Example 11 13.4 0.0 4.5 0.0 0.0 0.0 4.5
68.8 4.5 1.1 3.3 3.48 Ce2Ni7 1.8122 Example 12 13.8 0.0 3.1 0.0 0.0
0.0 3.7 71.1 4.1 1.0 3.1 3.85 Ce5Co19 1.8202 Example 13 16.5 0.0
2.1 0.0 0.0 0.0 2.1 71.1 4.1 1.0 3.1 3.85 Pr5Co19 1.8446 Example 14
17.2 0.0 0.0 0.0 0.0 0.0 4.3 71.0 4.3 0.0 3.2 3.65 Ce5Co19 1.822
Example 15 14.1 0.0 3.7 0.0 0.0 0.0 3.9 71.7 4.3 0.0 2.2 3.60
Pr5Co19 1.8192 Example 16 13.0 0.0 0.0 4.3 0.0 0.0 4.3 72.8 2.2 0.0
3.3 3.60 Pr5Co19 1.8108 Example 17 13.0 0.0 0.0 5.2 0.0 0.0 3.5
72.8 2.2 0.0 3.3 3.60 Pr5Co19 1.8196 Example 18 9.8 0.0 6.5 1.1 0.0
0.0 4.3 71.7 4.3 0.0 2.2 3.60 Pr5Co19 1.8045 Example 19 6.5 0.0
10.9 0.0 0.0 0.0 4.3 71.7 4.3 0.0 2.2 3.60 Ce2Ni7 1.7975 Example 20
12.8 0.0 0.0 3.2 0.0 0.0 5.3 72.3 4.3 0.0 2.1 3.70 PuNi3 1.7999
Example 21 12.8 0.0 0.0 5.3 0.0 0.0 3.2 72.3 4.3 0.0 2.1 3.70
Pr5Co19 1.8218 Example 22 17.9 0.0 0.0 1.1 0.0 0.0 2.3 72.3 4.3 0.0
2.1 3.70 Pr5Co19 1.844 Example 23 3.9 8.7 1.1 4.3 0.2 0.0 3.5 71.7
4.3 0.0 2.2 3.60 Ce2Ni7 1.7978 Example 24 14.0 0.0 0.0 2.1 0.0 2.1
3.0 73.4 2.1 1.1 2.1 3.70 Ce5Co19 1.8253 Example 25 12.5 0.0 0.0
0.0 0.0 4.2 4.2 69.8 6.3 0.0 3.1 3.80 Ce5Co19 1.8068 Example 26
12.9 0.0 0.0 0.0 0.0 4.6 3.3 69.8 6.3 0.0 3.1 3.80 Ce5Co19 1.8163
Example 27 14.8 0.2 0.0 0.0 0.0 2.9 2.9 69.8 6.3 0.0 3.1 3.80
Ce5Co19 1.8273 Example 28 15.8 0.0 0.0 0.0 0.0 2.5 2.5 69.8 6.3 0.0
3.1 3.80 Ce2Ni7 1.8349 Example 29 14.8 2.1 0.0 0.0 0.0 0.0 3.7 73.2
4.1 0.0 2.1 3.85 Ce5Co19 1.8223 Example 30 14.5 2.0 0.0 0.0 0.0 0.0
3.6 73.7 4.0 0.0 2.0 3.95 Ce5Co19 1.8223 Example 31 16.1 0.0 2.2
0.0 0.0 0.0 4.0 69.9 4.5 0.0 3.3 3.48 Ce2Ni7 1.8226 Example 32 11.0
0.0 0.0 6.6 0.0 0.0 4.4 69.1 5.5 0.0 3.3 3.53 Ce5Co19 1.8052
Example 33 11.2 0.0 0.0 6.7 0.0 0.0 4.5 69.9 4.5 0.0 3.3 3.48
Ce5Co19 1.8052 Example 34 12.8 0.0 4.3 0.0 0.0 0.0 4.3 70.2 4.3 0.0
4.3 3.70 Ce5Co19 1.8122 Example 35 16.3 0.0 0.0 0.0 0.0 0.0 5.4
71.7 4.3 0.0 2.2 3.60 PuNi3 1.8083 Example 36 13.9 0.0 0.0 4.8 0.0
0.0 3.0 71.4 4.3 0.0 2.6 3.62 Pr5Co19 1.8262 Example 37 13.9 0.0
0.0 4.3 0.0 0.0 3.5 71.4 4.3 0.0 2.6 3.62 Pr5Co19 1.8218 Example 38
14.1 0.0 0.0 4.3 0.0 0.0 3.2 71.4 4.3 0.0 2.6 3.62 Pr5Co19 1.8246
Example 39 15.2 0.0 0.0 3.2 0.0 0.0 3.2 71.4 4.3 0.0 2.6 3.62
Pr5Co19 1.8274 Example 40 15.4 0.0 0.0 3.3 0.0 0.0 3.3 71.1 4.4 0.0
2.6 3.56 Pr5Co19 1.8274 Example 41 16.4 0.0 0.0 2.2 0.0 0.0 3.3
71.1 4.4 0.0 2.6 3.56 Pr5Co19 1.8302 Example 42 3.8 0.0 7.6 7.6 0.0
0.0 3.3 73.3 0.0 0.0 4.4 3.50 Ce2Ni7 1.8001 Comparative 11.5 3.9
0.2 0.8 0.0 0.0 0.0 67.2 4.9 6.6 4.9 5.10 CaCu5 1.8612 example 2
Capacity Capac- retention E- Produced phase (%) ity ratio valu-
Ce2Ni7 Pr5Co19 Ce5Co19 La4MgNi24 CaCu5 Others mAh/g % ation Example
7 43 6 32 5 14 351 89.3 Example 8 18 34 21 21 6 352 94.5 Example 9
28 50 12 6 4 349 96 Example 10 40 42 10 4 4 347 95.4 Example 11 50
30 9 11 340 91.6 .largecircle. Example 12 32 17 44 7 354 92.9
.largecircle. Example 13 55 33 12 325 88.6 .DELTA. Example 14 20 28
42 10 355 91.3 .largecircle. Example 15 20 42 34 4 350 97 Example
16 10 45 40 5 348 97.5 Example 17 26 60 14 347 97.8 Example 18 36
40 20 4 350 96.5 Example 19 45 18 30 7 324 94.6 .largecircle.
Example 20 15 19 32 34 321 90.6 .DELTA. Example 21 58 36 6 354 97.5
Example 22 24 55 17 4 337 92.6 .DELTA. Example 23 39 19 32 10 325
88 .DELTA. Example 24 30 28 31 6 5 347 96 Example 25 22 15 40 10 13
360 92.7 .largecircle. Example 26 20 19 34 7 20 355 94.9 Example 27
18 22 31 5 6 18 350 94.1 Example 28 35 25 30 10 331 90.4 .DELTA.
Example 29 16 20 48 16 358 91.5 .largecircle. Example 30 20 58 22
352 91.3 .largecircle. Example 31 55 14 21 10 326 88.6 .DELTA.
Example 32 31 23 39 7 341 94.1 Example 33 37 11 41 11 331 92.1
.DELTA. Example 34 18 38 37 7 337 93 .largecircle. Example 35 21 13
29 37 341 88.9 .largecircle. Example 36 55 38 7 346 94.9 Example 37
7 47 43 3 348 95.2 Example 38 50 45 5 347 95 Example 39 53 44 3 352
95.3 Example 40 8 47 42 3 351 95.3 Example 41 39 26 35 357 90.6
.largecircle. Example 42 92 3 5 337 92.6 .DELTA. Comparative 100
307 97.5 .largecircle. example 2
[0136] With respect to the hydrogen storage alloys of Examples 7 to
42 and Comparative Example 2, the production ratios of the crystal
phases were calculated and cycle performance measurement was
carried out as same as Example 1. The maximum values of the
discharge capacity and retention ratios of discharge capacity at 50
cycles are shown in Table 5. Those having the maximum values of the
discharge capacity of 340 mAh/g or higher and retention ratio of
the discharge capacity at 93% or higher are marked with : those
which satisfy either one were marked with .smallcircle.: and those
which satisfy neither were marked with .DELTA.. The results are
shown together in Table 5.
[0137] Further, the calculation results of average atom radius rA
(.ANG.) of the above-mentioned R1. element and R2 element (elements
at A side) and the ratio (B/A) are shown together in Table 5 and
the graph formed by plotting the evaluation results in the B/A-rA
(.ANG.) coordinate is shown in FIG. 7.
[0138] As shown in FIG. 7, in the case of using the hydrogen
storage alloys of Examples which satisfy
3.53.ltoreq.(B/A).ltoreq.3.80 and
0.0593(B/A)+1.59.ltoreq.rA.ltoreq.0.0063(B/A)+1.81, that almost all
of them exhibited excellent discharge capacity and cycle
performance.
[0139] Further, from Table 5, in the case rA and B/A satisfy the
above-mentioned expressions, respectively, the main produced phase
tends to be Pr.sub.5Co.sub.19 phase or Ce.sub.5Co.sub.19 phase and
it was confirmed that excellent discharge capacity and cycle
performance were exhibited.
[0140] Furthermore, from Table 5, with respect to Examples 15 to
18, 21, 24 to 27, 32, 34, and 35 to 40 which satisfy the following:
the R1 is one or more kind elements R1' selected from a group
consisting of Ce, Pr, Nd, Sm, and Y and La at La/R1' ratio of 5 or
less; the R2 is Mg; the R4 is one or two elements selected from Ni
and Co; the R5 is Al; and d, e, f, and g respectively satisfy
16.ltoreq.d.ltoreq.19; 2.ltoreq.e.ltoreq.5; 73.ltoreq.f.ltoreq.78;
and 2.ltoreq.g.ltoreq.4, Pr5Co.sub.19 phase and Ce.sub.5Co.sub.19
phase were produced preferentially and the uniformity of the alloys
was improved.
Examples 43 to 81
[0141] Using the alloy raw materials of the compositions shown in
the following Table 6, hydrogen storage alloys of Examples 43 to 81
were produced in the same manner as Example 1. When the lattice
images of these hydrogen storage alloys were observed by a
transmission electron microscope (TEM), it was confirmed that
crystal phases with different crystal structures were layered in
the c-axis direction.
[0142] With respect to the obtained hydrogen storage alloys, the
production ratios of the crystal phases were calculated and cycle
performance (the maximum values of the discharge capacity and
retention ratios of discharge capacity at 50 cycles) measurement
was carried out as same as Example 1. The results are shown
together in Table 6. The above-mentioned La/R1' ratios are also
shown in Table 6.
TABLE-US-00006 TABLE 6 Alloy composition (mol %) La Ce Pr Nd Y Zr
Ti V Sn Zn Mg Ni Co Mn Al Fe Cu Si La/R1' Example 8.3 8.5 0.2 4.3
68.1 6.4 2.1 2.1 100 0.49 43 Example 11.7 5.1 0.2 4.3 68.1 6.4 2.1
2.1 100 0.70 44 Example 13.6 3.2 0.2 4.3 68.1 6.4 2.1 2.1 100 0.81
45 Example 14.3 2.6 0.2 4.3 68.1 6.4 2.1 2.1 100 0.85 46 Example
14.7 2.1 0.2 4.3 68.1 6.4 2.1 2.1 100 0.87 47 Example 16.8 0.0 0.2
4.3 68.1 6.4 2.1 2.1 100 1.00 48 Example 17.9 2.1 0.2 1.1 68.1 6.4
2.1 2.1 100 0.89 49 Example 16.8 2.1 0.2 2.1 68.1 6.4 2.1 2.1 100
0.89 50 Example 16.2 2.1 0.2 2.8 68.1 6.4 2.1 2.1 100 0.88 51
Example 13.6 2.1 0.2 5.3 68.1 6.4 2.1 2.1 100 0.86 52 Example 12.6
2.1 0.2 6.4 68.1 6.4 2.1 2.1 100 0.86 53 Example 13.4 4.3 0.2 3.4
68.1 6.4 2.1 2.1 100 0.76 54 Example 14.5 3.2 0.2 3.4 68.1 6.4 2.1
2.1 100 0.82 55 Example 14.5 3.2 0.2 3.4 68.1 6.4 2.1 2.1 100 0.82
56 Example 14.5 3.2 0.2 3.4 68.1 6.4 2.1 2.1 100 0.82 57 Example
14.5 3.2 0.2 3.4 68.1 6.4 2.1 2.1 100 0.82 58 Example 14.5 3.4 3.4
68.1 6.4 2.1 2.1 100 0.81 59 Example 14.5 2.8 0.6 3.4 68.1 6.4 2.1
2.1 100 0.84 60 Example 14.5 2.3 1.1 3.4 68.1 6.4 2.1 2.1 100 0.86
61 Example 14.5 3.2 0.2 3.4 68.1 6.4 2.1 2.1 100 0.82 62 Example
14.5 3.2 0.2 3.4 68.1 6.4 2.1 2.1 100 0.82 63 Example 14.5 3.2 0.2
3.4 68.1 6.4 2.1 2.1 100 0.82 64 Example 16.6 3.7 0.2 3.9 63.4 7.3
2.4 2.4 100 0.82 65 Example 15.1 3.3 0.2 3.6 66.7 6.7 2.2 2.2 100
0.82 66 Example 14.2 3.1 0.2 3.3 68.8 6.3 2.1 2.1 100 0.82 67
Example 13.3 2.9 0.2 3.1 70.6 5.9 2.0 2.0 100 0.82 68 Example 14.5
3.2 0.2 3.4 68.1 6.4 4.3 100 0.82 69 Example 14.5 3.2 0.2 3.4 68.1
4.3 2.1 2.1 2.1 100 0.82 70 Example 14.5 3.2 0.2 3.4 68.1 4.3 2.1
2.1 2.1 100 0.82 71 Example 14.5 3.2 0.2 3.4 68.1 4.3 2.1 2.1 2.1
100 0.82 72 Example 14.8 3.3 0.2 3.5 69.6 4.3 1.1 3.3 100 0.82 73
Example 14.5 3.2 0.2 3.4 70.2 4.3 1.1 3.2 100 0.82 74 Example 14.2
3.1 0.2 3.3 70.8 4.2 1.0 3.1 100 0.82 75 Example 13.9 3.1 0.2 3.3
71.4 4.1 1.0 3.1 100 0.82 76 Example 13.6 3.0 0.2 3.2 72.0 4.0 1.0
3.0 100 0.82 77 Example 14.9 4.0 0.0 3.1 74.7 0.0 3.3 100 0.79 78
Example 14.9 3.5 0.0 3.5 70.3 4.4 3.3 100 0.81 79 Example 14.6 3.4
0.0 3.4 68.8 4.3 2.2 3.2 100 0.81 80 Example 4.7 8.1 7.0 0.0 3.5
72.1 2.3 0.0 2.3 100 0.24 81 Capacity Produced phases (% by weight)
Capacity retention AB2 Ce2Ni7 Gd2Co7 Pr5Co19 Ce5Co19 CaCu5 Others
Total mAh/g ratio % Example 3 41 8 33 15 100 336 94.9 43 Example 1
39 10 40 10 100 360 96.4 44 Example 41 9 41 9 100 364 96.3 45
Example 38 12 37 13 100 368 96.1 46 Example 30 14 37 19 100 370 94
47 Example 26 15 35 24 100 365 93.1 48 Example 46 14 30 10 100 125
99.7 49 Example 45 17 29 9 100 252 99.5 50 Example 44 14 31 11 100
335 98.1 51 Example 20 35 45 100 331 93.6 52 Example 2 42 56 100
285 93.5 53 Example 30 66 4 100 363 97 54 Example 31 64 5 100 368
97.1 55 Example 23 21 48 8 100 357 95.1 56 Example 24 70 6 100 368
97 57 Example 4 4 20 62 10 100 369 95.9 58 Example 31 66 3 100 372
95 59 Example 5 24 52 17 2 100 351 96.9 60 Example 10 21 42 23 4
100 336 96.1 61 Example 31 64 5 100 361 96.9 62 Example 31 64 5 100
358 96.8 63 Example 31 64 5 100 361 97 64 Example 43 5 31 21 100
335 95.9 65 Example 61 18 21 100 342 97.1 66 Example 24 20 45 11
100 372 95.7 67 Example 3 38 29 30 100 375 95.1 68 Example 33 24 31
6 6 100 356 97.3 69 Example 32 44 21 3 100 346 95.1 70 Example 30
40 26 4 100 344 95.2 71 Example 28 46 20 6 100 340 96.1 72 Example
63 6 24 7 100 364 97.3 73 Example 55 4 31 10 100 366 97.1 74
Example 44 17 30 9 100 366 96.4 75 Example 24 21 42 13 100 361 95.4
76 Example 20 28 30 22 100 350 95 77 Example 28 55 12 5 100 366
97.4 78 Example 28 55 12 5 100 366 97.4 79 Example 33 44 12 7 4 100
364 97.1 80 Example 100 100 330 97 81
[0143] As shown in Table 6, when the hydrogen storage alloys
containing the crystal phase having the Ce.sub.5Co.sub.19 type
crystal structure and having a composition defined as
La.sub.hR6.sub.iR7.sub.iMg.sub.kR8m (wherein R6 is one or more kind
elements selected from a group consisting of rare earth metals
including Y and excluding La; R7 is one or more kind elements
selected from a group consisting of Zr, Ti, Zn, Sn and V; R8 is one
or more kind elements selected from a group consisting of Ni, Co,
Mn, Al, Cu, Fe, Cr, and Si; and h, i, j, k and m satisfy
0.ltoreq.j.ltoreq.0.65; 2.ltoreq.k.ltoreq.5.5;
0.70.ltoreq.h/(h+i).ltoreq.0.85; and h+i+j+k+m=100), that is, the
hydrogen storage alloy of Examples 44 to 46, Examples 54 to 60,
Examples 62 to 64, and Examples 66 to 80, were used, it was
confirmed that excellent discharge capacity and cycle performance
were exhibited.
Examples 82 to 91
[0144] Using the alloy raw materials of the compositions shown in
the following Table 7, hydrogen storage alloys of Examples 82 to 91
were produced in the same manner as Example 1. When the lattice
images of these hydrogen storage alloys were observed by a
transmission electron microscope (TEM), it was confirmed that
crystal phases with different crystal structures were layered in
the c-axis direction.
[0145] Further, with respect to the hydrogen storage alloys, the
production ratios of the crystal phases were calculated and cycle
performance measurement was carried out as same as Example 1. The
results are shown together in Table 7.
TABLE-US-00007 TABLE 7 Capac- ity reten- tion Composition ratio
Produced phases La Pr Nd Y Mg Ni Co Mn Al (%) CaCu5 Ce2Ni7 Gd2Co7
Ce5Co19 Pr5Co19 La5MgNi24 AuBe5 Example 82 17.0 0.0 0.0 0.0 4.3
68.1 6.4 0.0 4.3 87.5 36.9 0.0 0.0 37.7 14.9 0.0 10.5 Example 83
17.9 0.0 0.0 0.0 3.4 68.1 6.4 2.1 2.1 88.6 25.9 40.3 0.0 24.9 5.9
0.0 3.0 Example 84 17.0 0.0 0.0 0.0 4.3 67.0 6.4 2.1 3.2 88.2 35.2
12.8 0.0 36.2 9.7 0.0 6.0 Example 85 14.9 0.0 0.0 2.1 4.3 68.1 6.4
2.1 2.1 97.9 1.2 8.7 0.0 23.7 53.1 13.4 0.0 Example 86 12.8 0.0 5.1
0.0 3.4 67.0 8.5 0.0 3.2 96.0 2.9 13.1 0.0 17.0 67.0 0.0 0.0
Example 87 12.6 4.2 0.0 0.0 4.2 69.5 6.3 0.6 2.5 96.0 9.8 0.0 0.0
22.2 6.9 61.1 0.0 Example 88 12.8 4.3 0.0 0.0 4.3 68.1 6.4 0.0 4.3
94.2 11.8 0.0 0.0 69.1 9.0 7.1 3.0 Example 89 12.8 4.3 0.0 0.0 4.3
61.7 12.8 0.0 4.3 92.5 14.1 0.0 0.0 60.1 10.1 10.0 5.7 Example 90
12.4 4.1 0.0 0.0 4.1 69.1 6.2 2.1 2.1 91.6 21.7 42.9 0.0 19.7 15.7
0.0 0.0 Example 91 9.4 7.3 0.0 0.0 4.2 68.8 6.3 2.1 2.1 91.7 22.0
39.8 13.4 24.9 0.0 0.0 0.0
[0146] Further, with respect to the hydrogen storage alloys, based
on the results of Table 7, a graph showing the relation of the
capacity retention ratio to the production ratio of CaCu.sub.5
phase is shown in FIG. 8.
[0147] As shown in FIG. 8, in the case of using the hydrogen
storage alloys with 22% by weight or less of CaCu.sub.5 phase, that
is, the hydrogen storage alloys of Examples 85 to 91, it was
confirmed that the capacity retention ratios were further higher
values and particularly, in the case the CaCu.sub.5 phase was 5% by
weight or less, it was confirmed that the capacity retention ratios
became extremely high values.
Examples 92 to 101
[0148] Using the alloy raw materials of the compositions shown in
the following Table 8, hydrogen storage alloys of Examples 92 to
101 were produced in the same manner as Example 1. When the lattice
images of these hydrogen storage alloys were observed by a
transmission electron microscope (TEM), it was confirmed that
crystal phases with different crystal structures were layered in
the c-axis direction.
[0149] Further, with respect to the hydrogen storage alloys, the
production ratios of the crystal phases were calculated in the same
manner as Example 1. Furthermore, with respect to the hydrogen
storage alloys, using Siebert PCT measurement apparatus
(manufactured by Suzuki Syokan Co. Ltd., P73-07), the equilibrium
pressure at 80.degree. C. in case of H/M=0.5 of PCT curve
(pressure-composition isothermal curve) was calculated. Further,
after cells using the respective hydrogen storage alloys were left
at 45.degree. C. for 14 days, the remaining discharge capacity was
measured in the same manner as described above and the remaining
discharge capacity to the maximum discharge capacity was
calculated. The results are also shown in Table 8.
TABLE-US-00008 TABLE 8 Equilibrium Remaining pressure capacity
Composition (Mpa) (%) La Pr Nd Y Mg Ni Co Mn Al B/A Example 92
0.035 17.0 0.0 0.0 0.0 4.3 68.1 6.4 1.7 2.6 3.7 Example 93 0.045
73.51 17.0 0.0 0.0 0.0 4.3 70.2 6.4 1.1 1.1 3.7 Example 94 0.052
75.17 17.0 0.0 0.0 0.0 4.3 72.3 4.3 2.1 0.0 3.7 Example 95 0.064
74.32 12.8 4.3 0.0 0.0 4.3 71.3 4.3 3.2 0.0 3.7 Example 96 0.057
76.21 16.7 0.0 0.0 0.0 4.2 68.8 6.3 1.7 2.5 3.8 Example 97 0.047
74.98 12.8 4.3 0.0 0.0 4.3 68.1 6.4 1.7 2.6 3.7 Example 98 0.11
70.72 5.0 13.8 0.0 0.0 2.1 77.1 0.0 0.4 1.7 3.8 Example 99 0.13
69.11 12.9 0.0 0.0 4.3 4.3 77.4 0.0 0.0 1.1 3.65 Example 100 0.18
68.45 4.3 0.0 13.2 0.0 3.8 68.1 6.4 1.1 3.2 3.7 Example 101 0.068
71.33 8.4 8.4 0.0 0.0 4.2 69.5 4.2 5.3 0.0 3.75 Produced phases
Ce2Ni7 Gd2Co7 Ce5Co19 Pr5Co19 CaCu5 AuBe5 La5MgNi24 Total Example
92 14.59 0 14.47 9.84 8.03 0 53.06 100.0 Example 93 39.03 0 40.22
8.37 12.38 0 0 100.0 Example 94 36.3 0 32.6 18.4 12.7 0 0 100.0
Example 95 44.47 4.04 28.92 16.29 6.27 0 0 100.0 Example 96 14.39 0
18.53 8.62 16.34 0 42.12 100.0 Example 97 17.88 0 24.38 48.42 6 0
3.33 100.0 Example 98 30.22 0 39.67 13.89 16.23 0 0 100.0 Example
99 13.05 33.51 43.44 0. 10.02 0 0 100.0 Example 100 36.1 0 33.45
8.81 18.9 2.77 0 100.0 Example 101 20.54 0 30.23 29.64 19.6 0 0
100.0
[0150] Further, with respect to the respective hydrogen storage
alloys, based on the results in Table 8, a graph showing the
relation of the remaining discharge capacity to the hydrogen
equilibrium pressure is shown in FIG. 9.
[0151] As shown in FIG. 9, in the case of using the hydrogen
storage alloys with 22% by weight or less of CaCu.sub.5 phase and
having hydrogen equilibrium pressure of 0.07 MPa or lower, that is,
the hydrogen storage alloys of Examples 92 to 97, it was confirmed
that the remaining discharge capacity was high value.
Examples 102 to 109
[0152] Using the alloy raw materials of the compositions shown in
the following Table 9, hydrogen storage alloys of Examples 102 to
109 were produced in the same manner as Example 1. Herein, in
Example 102 and Example 108, respectively high purity materials
were used for sources of La, Ce, and Nd and in Examples 103 to 107
and Example 109 excluding the former, misch metal including La, Ce,
Pr, and Nd was used. When the lattice images of these hydrogen
storage alloys were observed by a transmission electron microscope
(TEM), it was confirmed that crystal phases with different crystal
structures were layered in the c-axis direction.
[0153] Next, using these hydrogen storage alloys for negative
electrodes, sealed cells were respectively produced and the cycle
life was measured for each sealed cell. The practical procedure was
as described below.
<Production of Negative Electrode>
[0154] An aqueous solution in which a thickener (methyl cellulose)
was dissolved and each hydrogen storage alloy powder were mixed and
further mixed with 0.8% by weight of a binder (styrene-butadiene
rubber) to obtain a paste which was applied to both faces of a
punched steel plate (thickness 35 pm) and dried and thereafter the
resulting steel plate was pressed to a prescribed thickness (0.3
mm) to obtain a negative electrode.
<Production of Positive Electrode>
[0155] An aqueous solution in which a thickener (carboxymethyl
cellulose) was dissolved and paste of an active material were
packed in a foamed nickel substrate and dried and thereafter, the
resulting substrate was pressed to a prescribed thickness (0.78 mm)
to obtain a positive electrode. A material used as the active
material was a material obtained by coating the surface of nickel
hydroxide containing 3% by weight of zinc and 0.5% by weight of
cobalt in form of a solid solution with 6% by weight of cobalt
hydroxide.
<Production of Sealed Cell>
[0156] A jelly roll was produced by spirally rolling the obtained
positive electrode and negative electrode at a ratio of positive
electrode capacity 1 to negative electrode capacity 1.25 while
inserting a separator between them and a positive electrode
terminal part and a current collection terminal were resistance
welded and thereafter, the jelly roll was housed in a cylindrical
metal case. Further, 1.81 ml of an electrolyte solution containing
8 mol/L KOH and 0.8 mol/L LiOH was injected and a cover made of a
metal and equipped with a safety valve was used for closing to
produce each sealed cell with 2500 mAh AA size.
<Cycle Test>
[0157] After the above-mentioned sealed cell was initially charged
at 200C and 0.02 It (A) (50 mA) for 10 hours, the cell was again
charged at 0.25 It (A) (625 mA) for 5 hours. Thereafter,
discharging at 20.degree. C. and 0.2 It (A) (500 mA) to cut off
voltage of 1 V and charging at 20.degree. C. and 0.2 It (A) (500
mA) for 6 hours were repeated 10 times and finally discharging was
carried out for chemical conversion treatment.
[0158] Thereafter, charging in condition of 0.5 It (A) and -dV=5
mV, 30 minute pause, and discharging (20.degree. C.) at 1 It (A) to
final voltage of 1V were repeated and the number of cycles when the
discharge capacity became 50% of the initial capacity was defined
as the cycle life.
[0159] The measurement results are shown in Table 9 and FIG.
10.
TABLE-US-00009 TABLE 9 Total ratio of Pr.sub.5Co.sub.19 phase,
Ce.sub.5Co.sub.19 phase, Alloy composition (mol %) and
Ce.sub.2Ni.sub.7 phase La Ce Pr Nd Mg Ni Co Al (% by weight) Cycle
life Example 102 14.1 0.0 0.0 4.3 3.3 72.8 2.2 3.3 98 350 Example
103 15.2 0.4 0.9 2.0 3.3 72.8 2.2 3.3 98 350 Example 104 14.8 0.7
0.9 2.2 3.3 72.8 2.2 3.3 98 350 Example 105 14.6 0.9 0.7 2.2 3.5
72.8 2.2 3.3 96 340 Example 106 14.8 1.3 0.4 2.0 3.3 72.8 2.2 3.3
95 280 Example 107 13.9 2.2 0.2 2.0 3.5 72.8 2.2 3.3 85 150 Example
108 13.9 4.3 0.0 0.0 3.5 72.8 2.2 3.3 76 50 Example 109 16.3 0.4
0.2 1.3 3.5 72.8 2.2 3.3 88 160
[0160] As shown in Table 9, with respect to the hydrogen storage
alloys of the invention, it was understood that even if misch metal
was used as a raw material, the cycle life could be maintained for
a relatively long time by controlling the Ce content to be 2.2 mol
% or lower. Particularly, in the case of Example 103 to Example 106
in which the Ce content was 1.3 mol % or lower and the total ratio
of Pr.sub.5Co.sub.19 phase, Ce.sub.5Co.sub.19 phase, and
Ce.sub.2Ni.sub.7 phase was 95% by weight or higher were found
having extremely excellent cycle life, similarly to the hydrogen
storage alloy of Example 102 containing a high purity material, Nd,
in a relatively high amount.
* * * * *