U.S. patent application number 11/679504 was filed with the patent office on 2008-04-10 for hydrogen-absorbing alloy for an alkaline storage battery.
This patent application is currently assigned to SAFT. Invention is credited to Patrick Bernard, Amelie Ferey, Bernard Knosp, Michel Latroche.
Application Number | 20080085209 11/679504 |
Document ID | / |
Family ID | 37136744 |
Filed Date | 2008-04-10 |
United States Patent
Application |
20080085209 |
Kind Code |
A1 |
Bernard; Patrick ; et
al. |
April 10, 2008 |
HYDROGEN-ABSORBING ALLOY FOR AN ALKALINE STORAGE BATTERY
Abstract
Therefore the invention provides a hydrogen-absorbing alloy
comprising at least one A.sub.5B.sub.19 type crystalline phase
having the formula R.sub.1-yMg.sub.yNi.sub.3.8.+-.0.1-zM.sub.z, in
which R represents one or more elements chosen from La, Ce, Nd or
Pr; M represents one or more elements chosen from Mn, Fe, Al, Co,
Cu, Zr, Sn and M does not contain Cr; 0.ltoreq.y.ltoreq.0.30;
z.ltoreq.0.5. The invention extends to an electrode comprising an
active ingredient comprising said alloy. It also extends to a
nickel metal hydride alkaline storage battery the negative
electrode of which comprises said alloy. The invention also relates
to the process for the manufacture of said alloy.
Inventors: |
Bernard; Patrick; (Bordeaux,
FR) ; Knosp; Bernard; (Bordeaux, FR) ;
Latroche; Michel; (Saint-Cyr-L'Ecole, FR) ; Ferey;
Amelie; (Bures-Sur-Yvette, FR) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SAFT
Bagnolet
FR
Centre National de la Recheche Scientifique
Paris Cedex
FR
|
Family ID: |
37136744 |
Appl. No.: |
11/679504 |
Filed: |
February 27, 2007 |
Current U.S.
Class: |
420/455 |
Current CPC
Class: |
H01M 4/26 20130101; C22C
19/03 20130101; H01M 4/383 20130101; H01M 4/242 20130101; Y02E
60/10 20130101; C01B 3/0057 20130101; Y02E 60/32 20130101; C22C
19/07 20130101 |
Class at
Publication: |
420/455 |
International
Class: |
C22C 19/03 20060101
C22C019/03 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2006 |
FR |
0601751 |
Claims
1. Hydrogen-absorbing alloy comprising at least one crystalline
phase of type A.sub.5B.sub.19 having the formula
R.sub.1-yMg.sub.yNi.sub.3.8.+-.0.1-zM.sub.z, in which: R represents
one or more elements chosen from La, Ce, Nd or Pr; M represents one
or more elements chosen from Mn, Fe, Al, Co, Cu, Zr, Sn and M does
not contain Cr; 0.ltoreq.y.ltoreq.0.30; z.ltoreq.0.5.
2. Alloy according to claim 1, in which the sum of the
stoichiometric indices of nickel and M is 3.8.
3. Alloy according to claim 1, in which y.ltoreq.0.25.
4. Alloy according to claim 1, in which y>0.15.
5. Alloy according to claim 1, in which z.ltoreq.0.30.
6. Alloy according to claim 1, in which the stoichiometric index of
each of the nickel substituents is less than or equal to 0.20.
7. Alloy according to claim 6, in which the stoichiometric index of
each of the nickel substituents is less than or equal to 0.15.
8. Alloy according to claim 1, in which M represents one or more
elements chosen from Co, Al and Mn.
9. Alloy according to claim 1, in which M is Co.sub.aAl.sub.b, with
a.ltoreq.0.15 and b.ltoreq.0.15.
10. Alloy comprising a crystalline phase A.sub.5B.sub.19 as defined
in claim 1, and the overall composition of which has the formula:
R.sub.1-uMg.sub.uNi.sub.t-vM.sub.v where 0.ltoreq.u.ltoreq.0.25;
3.5.ltoreq.t.ltoreq.4.3; v.ltoreq.0.5.
11. Alloy according to claim 10 in which the crystalline phase
A.sub.bB.sub.19 represents at least 50% by volume of the alloy.
12. Alloy according to claim 1, in which the equilibrium pressure
at 40.degree. C., for 1% by mass of hydrogen inserted, is less than
1.5 bar.
13. Alloy according to claim 1, in which the size of the particles
is characterized by a Dv 50% of 30 to 120 .mu.m, preferably of 50
to 100 .mu.m.
14. Alloy according to claim 1, in which the size of the particles
is characterized by a Dv 50% of 120 to 200 .mu.m.
15. Electrode comprising an active ingredient comprising the alloy
according to claim 1.
16. Electrode according to claim 15 also comprising an
yttrium-based compound.
17. Electrode according to claim 16, in which the yttrium compound
is an oxide such as Y.sub.2O.sub.3, an hydroxide such as
Y(OH).sub.3 or an yttrium salt.
18. Electrode according to claim 17, in which the mass of yttrium
represents from 0.1 to 2% of the mass of the alloy, preferably from
0.2 to 1% of the mass of the alloy, also preferably from 0.2 to
0.7% of the mass of the alloy.
19. Nickel metal hydride alkaline storage battery comprising with
at least one negative electrode according to claim 15.
20. Process for the manufacture of an alloy according to claim 1
comprising the stages of: melting the single elements of the alloy
quenching or hyperquenching.
21. Process for the manufacture of an alloy according to claim 1
comprising the stage of: sintering from the single elements of the
alloy or sintering from prealloys.
22. Process for the manufacture of an alloy according to claim 1
comprising a stage of mechanosynthesis.
23. Process according to claim 20 for the manufacture of an alloy
comprising an annealing stage.
Description
TECHNICAL FIELD
[0001] A subject of the invention is a hydrogen-absorbing alloy
comprising at least one crystalline phase of A.sub.5B.sub.19 type,
and an alkaline storage battery of nickel metal hydride type
comprising at least one negative electrode (anode) containing said
alloy. Such a battery possesses a higher electrochemical capacity
than the nickel metal hydride batteries of the prior art as well as
a longer life.
STATE OF THE ART
[0002] Portable applications have increasing requirements for
energy volume density and power, at a low cost as in wireless tools
for example. At present the batteries reach a limitation in terms
of energy volume density, due to the optimization of the energy
volume densities of each of the two electrodes constituting the
battery: positive electrode based on nickel hydroxide and negative
electrode based on hydrogen-absorbing alloy AB.sub.5. The capacity
by mass of an AB.sub.5 type alloy is limited to 300-320 mAh/g.
[0003] When optimization of the battery's capacity is carried out,
it is to the detriment of its life span. Conversely it is possible
to carry out optimization of the life span of the battery, but to
the detriment of the capacity by volume.
[0004] In order to increase the capacity by volume, compositions
such as the AB.sub.2 alloy families have been studied. However,
although their initial capacity is greater than that of an AB.sub.5
alloy, their power and their life spans are considerably reduced.
Recently certain manufacturers have proposed the use of an
A.sub.2B.sub.7 type alloy. The following documents describe
A.sub.2B.sub.7 type alloys.
[0005] JP2001-316744 describes a hydrogen-absorbing alloy having
the formula Ln.sub.1-xMg.sub.x(Ni.sub.1-yT.sub.y).sub.z in which Ln
is at least one element chosen from the lanthanide series, Ca, Sr,
Sc, Y, Ti, Zr and the quantity of lanthanium represents from 10 to
50 atomic % of the lanthanides.
[0006] T is at least one element chosen from Li, V, Nb, Ta, Cr, Mo,
Mn, Fe, Co, Al, Ga, Zn, Sn, In, Cu, Si, P and B; and x, y and z
satisfy the relationships: 0.05.ltoreq.x<0.20;
0.ltoreq.y.ltoreq.0.5 and 2.8.ltoreq.z.ltoreq.3.9.
[0007] JP2002-069554 describes a hydrogen-absorbing alloy of
formula R.sub.1-aMg.sub.aNi.sub.bCo.sub.cM.sub.d in which R
represents at least two rare earth elements. R can also contain
yttrium. M represents one or more elements chosen from Mn, Fe, V,
Cr, Nb, Al, Ga, Zn, Sn, Cu, Si, P and B. The stoichiometric indices
a, b, c and d satisfy the following relationships:
0.15<a<0.35; 0.ltoreq.c.ltoreq.1.5; 0.ltoreq.d.ltoreq.0.2;
and 2.9<b+c+d<3.5.
[0008] EP-A-1 026 764 describes a hydrogen-absorbing alloy of
formula AM.sub.X, where A can be a rare earth element and/or
magnesium and M is one or more elements which can be chosen from
Cr, Mn, Fe, Co, Ni, Al, Cu and Sn and x satisfies the relationship:
2.7<x<3.8.
[0009] U.S. Pat. No. 6,214,492 describes a hydrogen-absorbing alloy
comprising at least one crystalline phase consisting of a unit cell
possessing at least one A.sub.2B.sub.4 type sub-cell, and at least
one AB.sub.5 type sub-cell. This alloy can optionally comprise a
type AB.sub.3 or type AB.sub.3.5 crystalline phase.
[0010] US2004/0134569 describes a hydrogen-absorbing alloy of
formula Ln.sub.1-xMg.sub.xNi.sub.y-aAl.sub.a in which Ln is at
least one rare earth element; and x, y and a satisfy the
relationships: 0.05.ltoreq.x<0.20; 2.8.ltoreq.y.ltoreq.3.9 and
0.10.ltoreq.a.ltoreq.0.25.
[0011] US2004/0146782 describes a hydrogen-absorbing alloy of
formula Ln.sub.1-xMg.sub.xNi.sub.y-aAl.sub.a in which Ln is at
least one rare earth element; M is chosen from the group consisting
of Al, V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si and P;
and x, y and a satisfy the relationships: 0.05.ltoreq.x<0.20;
2.8.ltoreq.y.ltoreq.3.9 and 0.10.ltoreq.a.ltoreq.0.50.
[0012] US2005/0100789 describes a hydrogen-absorbing alloy of
formula RE.sub.1-xMg.sub.xNi.sub.yAl.sub.zM.sub.a in which RE is a
rare earth element; M is an element other than a rare earth, and x,
y, z and a satisfy the relationships: 0.10.ltoreq.x<0.30;
2.8.ltoreq.y.ltoreq.3.6; 0.ltoreq.z.ltoreq.0.30and
3.0.ltoreq.y+z+a.ltoreq.3.6.
[0013] US2005/0175896 describes a hydrogen-absorbing alloy of
formula Ln.sub.1-xMg.sub.xNi.sub.y-aAl.sub.a in which Ln is a rare
earth element; and x, y and a satisfy the relationships:
0.05.ltoreq.x<0.20; 2.8.ltoreq.y.ltoreq.3.9; and
0.10.ltoreq.a.ltoreq.0.25.
[0014] Preferably, a part of the rare earth element or Ni is
substituted by at least one element chosen from the group
consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu,
Si, P and B.
[0015] US2005/0164083 describes a hydrogen-absorbing alloy of
formula Ln.sub.1-xMg.sub.xNi.sub.y-aAl.sub.a in which Ln is at
least one rare earth element, and x, y and a satisfy the
relationships: 0.15.ltoreq.x.ltoreq.0.25; 3.0.ltoreq.y.ltoreq.3.6;
and 0<a.ltoreq.0.3.
[0016] Preferably, a part of the rare earth element or Ni is
substituted by at least one element chosen from the group
consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu,
Si, P and B.
[0017] JP 09-194971 describes a hydrogen-absorbing alloy
represented by the formula:
R.sub.2(Ni.sub.7-X-Y-ZMn.sub.XA.sub.YB.sub.Z).sub.n in which R is a
rare earth element or a misch metal; A is one or more elements
chosen from Co, Cr, Fe, Al, Zr, W, Mo, and Ti; B is one or more
elements chosen from Cu, Nb and V; X, Y, Z and n satisfy the
relationships: 0.3.ltoreq.X.ltoreq.1.5; 0.ltoreq.Y.ltoreq.1.0;
0.ltoreq.Z.ltoreq.1.0; Y+Z.ltoreq.1.0;
0.96.ltoreq.n.ltoreq.1.1.
[0018] EP-A-0 783 040 describes a hydrogen-absorbing alloy of
formula
[0019] (R.sub.1-xL.sub.x)(Ni.sub.1yM.sub.y), in which R represents
La, Ce, Pr or Nd; L represents Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y,
Sc, Mg or Ca; M represents Co, Al, Mn, Fe, Cu, Zr, Ti, Mo, Si, V,
Cr, Nb, Hf, Ta, W, B or C; and x, y and z satisfy the
relationships: 0.05.ltoreq.x.ltoreq.0.4; 0.ltoreq.y.ltoreq.0.5; and
3.0.ltoreq.z.ltoreq.4.5.
[0020] JP 2004-115870 describes a hydrogen-absorbing alloy of
formula Ln.sub.1-xMg.sub.xNi.sub.yM.sub.z in which Ln is Y, Sc or a
rare earth element; M is Co, Mn, Al, Fe, V, Cr, Nb, Ga, Zn, Sn, Cu,
Si, P or B, and x, y, and z satisfy the relationships:
0.1.ltoreq.x.ltoreq.0.5; 2.5.ltoreq.y.ltoreq.3.5 and
0.ltoreq.z<0.5; and 3.0.ltoreq.y+z.ltoreq.3.5.
[0021] However, although the initial capacity of the A.sub.2B.sub.7
alloys is greater than that of an AB.sub.5 alloy and comparable to
that of an AB.sub.2 alloy, their life span is limited.
[0022] A nickel metal hydride type alkaline storage battery is
therefore sought, possessing a higher capacity than that of the
batteries of the prior art as well as a long life span.
SUMMARY OF THE INVENTION
[0023] The invention therefore provides a hydrogen-absorbing alloy
comprising at least one A.sub.5B.sub.19 type crystalline phase
having the formula R.sub.1-yMg.sub.yNi.sub.3.8.+-.0.1-zM.sub.z, in
which:
[0024] R represents one or more elements chosen from
[0025] La, Ce, Nd or Pr;
[0026] M represents one or more elements chosen from
[0027] Mn, Fe, Al, Co, Cu, Zr, Sn and M not containing Cr;
[0028] 0.ltoreq.y.ltoreq.0.30;
[0029] z.ltoreq.0.5.
[0030] The invention extends to an electrode comprising an active
material comprising said alloy. It also extends to a nickel metal
hydride alkaline storage battery comprising at least one negative
electrode comprising said alloy.
[0031] The invention also relates to the production process of said
alloy.
DETAILED DISCLOSURE OF EMBODIMENTS OF THE INVENTION
[0032] The hydrogen-absorbing alloy according to the invention
contains at least one A.sub.5B.sub.19 type crystalline phase,
corresponding to the formula:
R.sub.1-yMg.sub.yNi.sub.3.8.+-.0.1-zM.sub.z, where
[0033] R represents one or more elements chosen from La, Ce, Nd or
Pr;
[0034] M represents one or more nickel substituents chosen from the
elements Mn, Fe, Al, Co, Cu, Zr, Sn, and M does not contain the
element Cr.
[0035] 0.ltoreq.y.ltoreq.0.30;
[0036] z.ltoreq.0.5.
[0037] The presence of the element Cr as a nickel substituent is
excluded from the invention as the presence of Cr reduces the power
supplied by the battery.
[0038] The composition of the alloy can be confirmed by elementary
analysis (atomic absorption, inductive plasma technique), X-ray
diffraction, electron probe microanalysis (EPMA) with wavelength
dispersive spectroscopy (WDS).
[0039] According to a preferred embodiment, the sum of the
stoichiometric indices of nickel and M is 3.8.
[0040] According to an embodiment, y.ltoreq.0.25.
[0041] According to an embodiment, y>0.15.
[0042] According to an embodiment, z.ltoreq.0.30.
[0043] According to an embodiment, the stoichiometric index of each
of the nickel substituents is less than or equal to 0.20;
preferably it is less than or equal to 0.15.
[0044] According to an embodiment, M represents one or more
elements chosen from Co, Al and Mn.
[0045] According to a preferred embodiment, M is Co.sub.aAl.sub.b,
with a.ltoreq.0.15 and b.ltoreq.0.15.
[0046] According to an embodiment, the hydrogen-absorbing alloy
comprises the A.sub.5B.sub.19 crystalline phase as described
previously and its overall composition has the formula:
R.sub.1-uMg.sub.uNi.sub.t-vM.sub.v, where
[0047] 0.ltoreq.u.ltoreq.0.25;
[0048] 3.5.ltoreq.t.ltoreq.4.3;
[0049] v.ltoreq.0.5.
[0050] According to a preferred embodiment, the proportion of
A.sub.5B.sub.19 crystalline phase represents at least 50% by volume
of the alloy.
[0051] According to a second preferred embodiment, the equilibrium
pressure at 40.degree. C. for 1% by mass of hydrogen inserted is
less than 1.5 bar.
[0052] According to an embodiment, the size of the
hydrogen-absorbing alloy particles is characterized by a Dv 50% of
30 to 120 .mu.m, preferably of 50 to 100 .mu.m. According to
another embodiment, the size of the particles of hydrogen-absorbing
alloy is characterized by a Dv 50% of 120 to 200 .mu.m.
[0053] The alloy of the invention can be prepared by the following
three processes:
[0054] by melting the constitutive single elements of the alloy
followed by slow freezing (standard metallurgy), by quenching
(rapid freezing) as strip casting on a single roll or between
double rolls, by hyperquenching (ultra-rapid cooling) using melt
spinning techniques or rapid freezing on a single roll or between
doubles rolls ("planar flow casting")
[0055] by powder metallurgy (sintering) from single elements or
prealloys,
[0056] by mechanosynthesis.
[0057] Other alloy manufacturing processes can also be
envisaged.
[0058] The alloy of the invention may have undergone annealing.
[0059] The invention also proposes an electrode comprising an
active ingredient comprising the alloy as described previously. The
invention extends to a nickel metal hydride alkaline storage
battery comprising at least one negative electrode comprising the
alloy according to the invention.
[0060] It is advantageous, in order to obtain a still longer life
span of the negative electrode, to mix a yttrium compound with the
active ingredient containing the alloy. This compound can be an
yttrium oxide, hydroxide or salt.
[0061] The yttrium-based compound is chosen from a non-exhaustive
list comprising an yttrium-based oxide such as Y.sub.2O.sub.3, an
yttrium-based hydroxide such as Y(OH).sub.3 or a yttrium-based
salt. Preferably, the yttrium-based compound is yttrium oxide
Y.sub.2O.sub.3.
[0062] The yttrium-based compound is mixed with the alloy in a
proportion such that the mass of yttrium represents from 0.1 to 2%
of the mass of the alloy, preferably from 0.2 to 1% of the mass of
alloy, preferably also from 0.2 to 0.7% of the mass of the
alloy.
[0063] The process of addition of the yttrium-based compound to the
active ingredient during the manufacture of the anode is simple to
implement industrially. It does not require complex devices.
[0064] The anode is manufactured by covering an electrically
conductive support with a paste made up of an aqueous mixture of
the composition of active ingredient according to the invention and
additives.
[0065] The support can be a nickel foam, a flat or
three-dimensional perforated strip made of nickel or nickel-plated
steel.
[0066] The additives are intended to facilitate the use or the
performances of the anode. They can be thickeners such as
carboxymethyl cellulose (CMC), hydroxypropylmethyl cellulose
(HPMC), polyacrylic acid (PAA), poly(ethylene oxide) (PEO). They
can also be binders such as butadiene-styrene (SBR) copolymers,
polystyrene acrylate (PSA), polytetrafluoroethylene (PTFE). They
can also be polymer fibres, such as polyamide, polypropylene,
polyethylene, etc., in order to improve the mechanical properties
of the electrode. They can also be conductive agents such as nickel
powder, carbon powder or fibres, nanotubes.
[0067] Advantageously, the anode is covered with a surface layer
intended to improve high-speed discharge and/or recombination with
oxygen at the end of charging. The invention also relates to a
nickel metal hydride alkaline storage battery comprising said at
least one anode.
[0068] The battery according to the invention typically comprises
at least one anode, at least one nickel cathode, at least one
battery separator and an alkaline electrolyte.
[0069] The cathode is constituted by the active cathode mass
deposited on a support which can be a sintered support, a nickel
foam, a flat or three-dimensional perforated strip made of nickel
or nickel-plated steel.
[0070] The active cathode mass comprises the active cathode
ingredient and additives intended to facilitate its implementation
or its performances. The active cathode ingredient is a nickel
hydroxide Ni(OH).sub.2 which can be partially substituted by Co, Mg
and Zn. This hydroxide can be partially oxidized and can be coated
with a surface layer based on cobalt compounds.
[0071] Among the additives there can be mentioned, without this
list being exhaustive, carboxymethyl cellulose (CMC),
hydroxypropylmethyl cellulose (HPMC), hydroxypropyl cellulose
(HPC), hydroxyethyl cellulose (HEC), polyacrylic acid (PAA),
polystyrene maleic anhydride (SMA), optionally carboxylated
butadiene-styrene copolymers (SBR), a copolymer of acrylonitrile
and butadiene (NBR), .alpha. copolymer of styrene, ethylene,
butylene and styrene (SEBS), a terpolymer of styrene, butadiene and
vinylpyridine (SBVR), polystyrene acrylate (PSA),
polytetrafluoroethylene (PTFE), a fluorinated copolymer of ethylene
and propylene (FEP), polyhexafluoropropylene (PPHF), ethylvinyl
alcool (EVA), zinc oxide ZnO, fibres (Ni, C, polymers), powders of
compounds based on cobalt such as Co, Co(OH).sub.2, CoO,
Li.sub.xCoO.sub.2, H.sub.xCoO.sub.2, Na.sub.xCoO.sub.2.
[0072] The battery separator is generally composed of polyolefin
fibres (e.g. polypropylene) or nonwoven porous polyamide.
[0073] The electrolyte is a concentrated alkaline aqueous solution
comprising at least one hydroxide (KOH, NaOH, LiOH), in a
concentration generally of the order of several times
normality.
[0074] The electrode pastes are prepared in a standard fashion, the
electrodes are manufactured, then at least one cathode, a battery
separator and an anode are superposed in order to constitute the
electrochemical bundle. The electrochemical bundle is introduced
into a container and impregnated with an aqueous alkaline
electrolyte. The battery is then closed.
[0075] The invention relates to any format of batteries: prismatic
format (flat electrodes) or cylindrical format (spiral or
concentric electrodes).
[0076] The battery according to the invention can be of the open
(open or semi-open) type or of the sealed type.
[0077] The battery according to the invention is particularly well
suited as an energy source for an electric vehicle or a portable
device.
EXAMPLES
[0078] Alloys, the overall composition of which has the formula
(La, Ce, Nd, Pr).sub.1-uMg.sub.u(Ni, Mn, Al, Co).sub.t, are
produced by sintering prealloys
[0079] (La, Ce, Nd, Pr)(Ni, Mn, Al, Co).sub.x (1<x<=5) and
Mg.sub.2Ni in sealed crucibles under argon and annealed at
temperatures comprised between 800 and 1100.degree. C. for periods
comprised between 1 hour and 10 days.
[0080] The elemental composition of these alloys is indicated in
Table 1 TABLE-US-00001 TABLE 1 Elemental composition of the alloys
Al- loy La Ce Nd Pr Mg Ni Mn Al Co t A 0.7 0 0 0 0.30 2.80 0 0 0.5
3.3 B 0.20 0 0.20 0.45 0.15 3.58 0.02 0.05 0.05 3.7 C 0.60 0.18
0.07 0.03 0.12 4.02 0.13 0.10 0.25 4.5
[0081] The alloy of Example A of the prior art is characterized by
an Mg level equal to u=0.30, a value of t=3.3 and a value of
v=0.5.
[0082] The alloy of Example B according to the invention has a
magnesium level of u=0.15, a stoichiometry of t=3.7, and a partial
substitution of the nickel by Mn, Al and Co at the level
v=0.12.
[0083] The magnesium level of the alloy C which is outside the
invention is equal to u=0.12, its stoichiometry is equal to t=4.5
and the nickel is substituted by Mn, Al and Co at the level
v=0.48.
[0084] The composition of the alloys in terms of crystalline phases
is determined using the trace of X-ray diffraction diagrams, using
the copper wavelength K.alpha..sub.1. The composition in terms of
crystalline phases is determined by following the Rietveld method
(Rietveld, H. M., A profile refinement method for nuclear and
magnetic structures. Journal of Applied Crystallography, 1969, 2,
6571). The compositions of alloys A, B and C in terms of
crystalline phases are shown in Table 2. TABLE-US-00002 TABLE 2
Composition of the alloys in terms of phases. Phase (%) Alloy Type
A.sub.2B.sub.7(R) Type A.sub.2B.sub.7(H) Type A.sub.5B.sub.19(R)
Type AB.sub.5(H) A 0 100 0 0 B 9 1 82 8 C 11 7 24 58
[0085] The alloy of Example A of the prior art is constituted only
by a hexagonal A.sub.2B.sub.7 phase A.sub.2B.sub.7(H) of
Ce.sub.2Ni.sub.7 type.
[0086] The alloy of Example B according to the invention comprises
10% A.sub.2B.sub.7 type phases (hexagonal of Ce.sub.2Ni.sub.7 type
or rhombohedral of Gd.sub.2Co.sub.7 type,), 8% hexagonal AB.sub.5
phase of CaCu.sub.5 type and 82% rhombohedral A.sub.5B.sub.19 type
phase of Ce.sub.5Co.sub.19 type.
[0087] The alloy C which is outside the invention is characterized
by the presence of 24% A.sub.5B.sub.19 phase, 18% A.sub.2B.sub.7
phase and 58% AB.sub.5 phase.
[0088] A sample of alloy is coated with an epoxy resin, then
polished. Different points on the polished sample are analyzed
using a electronic microprobe with wavelength dispersive analysis
in order to determine its composition. The B/A ratio where B is the
sum of the level of Ni and of the element(s) M, and A is the sum of
the La, Ce, Nd, Pr and Mg levels, is determined for each point
analyzed.
[0089] The results of the analysis by electronic microprobe of the
A.sub.5B.sub.19 phase of alloys A, B and C are shown in Table 3.
TABLE-US-00003 TABLEAU 3 Composition of the A.sub.5B.sub.19 phase
of the alloys. Alloy La Ce Nd Pr Mg Ni Mn Al Co B/A A No
A.sub.5B.sub.19 phase B 0.16 0.14 0.39 0.19 3.58 0.03 0.06 0.07
3.74 C 0.45 0.12 0.05 0.02 0.21 3.31 0.12 0.14 0.28 3.85
[0090] The alloy A of the prior art does not contain any
A.sub.5B.sub.19 phase.
[0091] The A.sub.5B.sub.19 phase of the alloy B according to the
invention has an Mg level y equal to 0.19 and a level z of element
M equal to 0.16.
[0092] The A.sub.5B.sub.19 phase of the alloy C which is outside
the invention has an Mg level y equal to 0.21 and a level z of
element M equal to 0.54.
[0093] The mass capacity of the alloys is determined in prismatic
laboratory elements the capacity of which is limited by the
anode.
[0094] The anodes comprising the alloys are constituted by a
mixture of:
[0095] 65% (by weight) of the alloy reduced to powder the particle
size distribution of which is characterized by a Dv 50%
corresponding to a size of 40 .mu.m
[0096] 30% (by weight) of nickel powder as conductive compound
[0097] 5% of PTFE as binder.
[0098] Yttrium oxide is added to the anode 3 of Table 4, at a level
of 0.5% yttrium with respect to the alloy mass.
[0099] The cathode comprises a standard nickel foam type current
collector and an active ingredient constituted by a nickel
hydroxide partially substituted by Zn and Co, the conductive
network of which, constituted by Co(OH).sub.2 has been formed
beforehand.
[0100] The anode and the cathode are separated by a polyolefin
battery separator and a membrane intended to prevent any
recombination of oxygen, released at the cathode, on the anode.
[0101] The electrolyte is an aqueous solution of KOH at 8.7
mole/litre.
[0102] After a first charge for 16 hours with a current of 40 mA
per gram of alloy (charge for 16 hours at 40 mA/g), the alloy is
activated over 10 cycles under the following conditions:
[0103] Discharge at 80 mA/g, cut-off voltage=0.9 V.
[0104] recharge for 16 hours at 40 mA/g
[0105] rest for 1 hour.
[0106] Then the batteries are cycled under the following
conditions:
[0107] discharge for 48 minutes at 400 mA/g, cut-off voltage=0.9
V.
[0108] recharge for 52 minutes at 400 mA/g.
[0109] By alloy life span is meant the number of cycles
corresponding to a discharged capacity equal to 80% of the maximum
capacity measured during the activation period.
[0110] The capacities and life span in an open element is shown in
Table 4. TABLE-US-00004 TABLE 4 Discharged initial capacity and
life span of the anodes Anode 1 2 3 4 Alloy A B B C Y.sub.2O.sub.3
(Y/alloy = 0.5% by mass) no no yes no Q (mAh/g) 367 358 355 323
Life span (cycles) 153 257 398 174
[0111] The maximum capacity restored during activation by the anode
1 for which the active ingredient is the alloy A of the prior art
is equal to 367 mAh/g. However, it decreases rapidly during cycling
in order to reach 80% of the initial capacity at cycle 153.
[0112] The maximum capacity restored during activation by the anode
2 for which the active ingredient is the alloy B of the invention
is equal to 358 mAh/g. The life span of this anode 2 is 257
cycles.
[0113] The anode 3 contains alloy B of the invention and yttrium
oxide. The maximum capacity restored during the activation by this
series is 355 mAh/g and its life span is 398 cycles.
[0114] The capacity of the anodes 2 and 3 is greater than 320
mAh/g, which is the mass capacity of the NiMH batteries of the
prior art.
[0115] The addition of yttrium oxide to the anode 3 makes it
possible to prolong the life span of the anode by 141 cycles
compared with the anode 2.
[0116] The maximum capacity restored during activation by the anode
4, for which the active ingredient is the alloy C which is outside
the invention, is equal to 323 mA/g. This is attributed to the
large quantity of AB.sub.5 type phase contained in this alloy. Its
life span is limited to 174 cycles.
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