Note: Descriptions are shown in the official language in which they were submitted.
12~L;9083
Thi~ is a divisional application of copending application
477,392, filed March 25, 1985.
The subject matter of this invention relates to the
field of energy storage and utilization with novel composi-
tions of matter that reversibly store hydrogen as a source
of electrochemical energy for subsequent release to produce
an electrical current. More particularly, novel active
material compositions, processes of making the active
material, fabrication and assembly of electrodes, cells,
and batteries are disclosed herein.
Some research has been conducted involving hydrogen
storage secondary batteries. However, a basic understand-
ing resulting in a viable approach to optimizing such
batteries has not been forthcoming in the scientific or
patent literature. Examples of such efforts are U.S.
Patents Nos. 3,669,745 and 3,824,131 and a technical paper
entitled "A New Type of Reversible Negative Electrode for
Alkaline Storage Batteries Based on Metal Alloy Hydrides,"
1974, 8th International Power Sources Conference. These
research efforts have not resulted in widespread commercial
utilization of this battery technology. In fact, the
prior research suggests no significant improvement over
conventional battery systems such as nickel cadmium. As a
result, the hydrogen storage battery system has apparently
been ignored or abandoned.
Secondary batteries using a hydrogen rechargeable
electrode operate in a different manner than lead acid,
nickel cadmium, or other battery systems. The hydrogen
storage battery utilizes an anode which is capable of
reversibly electrochemically storing hydrogen and usually
employs a cathode of nickel hydroxide material. The anode
and cathode are spaced apart in an alkaline electrolyte.
Upon application of an electrical current to the anode,
the anode material (M) is charged by the absorption of
hydrogen:
M + H20 + e < M-H + OH
: .
.
~, ~ ` - ` ' : `
:' ~
' - ` '
.
.
.
--2--
Upon discharge the stored hydrogen is released to provide
an electric current:
M-H + OH < M + H20 + e
The reactions are reversible and this is also true of the
reactions which take place at the cathode. As an example,
the reactions at a conventional nickel hydroxide cathode
as utilized in a hydrogen rechargeable secondary battery
are as follows:
Charging: Ni(OH)2 + OH < NiOOH + H20 + e
Discharging: NiOOH + H20 + e < Ni(OH)2 + OH
The battery utili~ing an electrochemically hydrogen
rechargeable anode offers important potential advantages
over conventional secondary batteries. Hydrogen recharge-
able anodes should offer significantly higher specific
charge capacities than lead anodes or cadmium anodes.
Furthermore, lead acid batteries and nickel-cadmium type
secondary batteries are relatively inefficient, because of
their low storage capacity and cycle life. A higher
energy density should be possible with hydrogen storage
batteries than these conventional systems, making them
particularly suitable for battery powered vehicles and
other mobile applications. Hydrogen storage batteries
have not lived up to their potential, however, because of
the materials and mechanical structures used.
An example of hydrogen storage materials which are
not readily useable for battery applications is found in
Japanese Patent Application No. Sho53-164130 which was
published July 11, 1980. A hydrogen storage metal mate-
rial is disclosed with the composition formula (Vl XTix)3
Ni1 yMy, whereas M is Cr, Mn, Fe; 0.05 ~= x <= 0.8 and
O <= y <= 0.6. The temperature and pressure conditions
for using this material for effective hydrogen storage,
however, exceed the normal conditions at which com-
mercially acceptable batteries safely operate. Other
0~3
--3--
problems, like corrosion also must be alleviated if these
hydrogen storage materials are used in a battery.
The preparation of hydrogen storage materials and
fabrication of electrodes also are of utmost importance.
It is desirable that the hydrogen storage materials be
somewhat homogeneous to provide uniformity in their elec-
trochemical properties. Often the individual components
of the hydrogen storage materials are combined by melting
the components together to form a bulk material such as an
ingot. The hydrogen storage materials produced in this
form are unsuitable for immediate use without further
processing. Reducing the size of these bulk materials for
fabrication as an electrode, however, can be quite diffi-
cult because of the unusual hardness and ductility of many
hydrogen storage materials. Normal size reduction tech-
nigues which use such devices as jaw crushers, mechanical
attritors, ball mills, and fluid energy mills often fail
to economically reduce the size of such hydrogen storage
materials. Thus, grinding and crushing operations for
these materials have been complicated and the results have
not been uniform.
Attempts to make metals brittle in order to crush
them more easily are not new in the art. Prior methods,
however, have involved mechanical addition of embrittling
agents, the presence of which would have an undesirable
effect on the electrochemical properties of the hydrogen
storage materials.
Other methods for embrittling metals are disclosed in
Canadian Patent No. 533,208 granted to Brown. This patent
identifies many disadvantages of treating vanadium metal
with hydrogen gas to facilitate its crushing and, instead,
recommends using cathodic charging as a successful size
reduction technique. Although one is dissuaded from using
hydrogen gas by the Brown patent, the present invention
` 1'~tj~083
.
--4--
overcomes the disadvantages to provide a useful and com-
mercially desirable technique of size reduction.
The previous attempts to utilize hydrogen storage
materials in secondary batteries have proven unsuccessful
because of the materials' poor electrochemical performance,
structural instability, and expensive fabrication. The
invention herein provides a new and improved battery and
method of fabricating the same with an electrode incor-
porating an active material composition and structure
allowing for high charge and discharge rates, efficient
reversibility, high electrical efficiency, bulk hydrogen
storage without substantial structural change or poison-
ing, mechanical integrity over long cycle life, and deep
discharge capability.
The present invention includes an active material for
an hydrogen storage electrode. The problems in prior art
hydrogen storage materials discussed above are obviated by
the present invention, all with improved electrochemical
performance of the electrodes, cells, and batteries incor-
porating the novel active materials. The composition
formula of the active material is selected from the group
consisting of:
a.) (TiV2_XNix)l_yMy
whereas, 0.2 <= x <= 1.0, 0 ~= y ~= 0.2 and M = Al or Zr;
b.) Ti2-xzrxv4-yNiy
whereas, 0 < x <= 1.5, 0.6 <= y <= 3.5; and
c.) Til xCrxV2 yNiy
whereas, 0 < x <= 0.75, 0.2 <= y <= 1Ø
The active materials of the present invention also
have the following novel compositions. A first group of
active material compositions incorporate the elements of
titanium present in an amount between about 28 and 36
atomic percent, vanadium present in an amount between
about 40 and 56 atomic percent and nickel present in an
amount between about 10 and 22 atomic percent. A second
' ~
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` 1;~tj9083
-5-
composition group incorporates the elements of titanium
present in an amount between about 15 and 20 atomic per-
cent, vanadium present in an amount between about 15 and
40 atomic percent, zirconium present in an amount between
about 10 and 20 atomic percent, and nickel present in an
amount between about 30 and 55 atomic percent. A pre-
ferred third composition group incorporates titanium
present in an amount between about 15 and 25 atomic per-
cent, vanadium present in an amount between about 45 and
55 atomic percent, chromium present in an amount between
about 5 and 25 atomic percent, and nickel present in an
amount between about 10 and 25 atomic percent.
The active materials provided by the present inven-
tion also have novel structures. These materials may be
single or multiphase combinations of amorphous, micro-
crystalline, or polycrystalline structures. Preferably,
these materials have a multiphase polycrystalline struc-
ture. An active material for hydrogen storage electrode
is provided by the present invention including a grain
phase having means for reversibly storing hydrogen and a
primary intergranular phase having means for catalyzing
hydrogen oxidation. The primary intergranular phase is in
operative contact with the grain phase.
The present invention provides an electrode for use
in an electrochemical cell and a battery including a
plurality of such electrochemical cells. The active
material incorporated in each of these devices is
described above.
A method of making an electrode using a hydrogen
storage active material is also contemplated by the
present invention. This method includes providing an
active material of the composition and/or structure
described above in a predetermined particle size distri-
bution, and subse~uently, fabricating an electrode with
the sized material.
.
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9083
-6-
The present invention also provides a method of
making hydrogen storage active material for use in an
electrode. The method includes the steps of providing an
active material in bulk form having means for reversibly
storing hydrogen and a homogeneous phase structure.
Additional steps include hydriding the bulk material,
dehydriding the bulk material, and pulverizing the bulk
material to a predetermined particle size distribution.
The present invention also includes the method of
sizing a hydride-forming metallic alloy. The method
includes the steps of providing a hydride-forming metallic
alloy in bulk form and hydriding the bulk alloy. Then the
method includes dehydriding the bulk alloy and pulverizing
the alloy to a predetermined particle size distribution.
We have found that the above disadvantages may be
overcome by use of active materials for a hydrogen storage
electrode which have composition formulae selected from
the group consisting of:
a.) (TiV2_XNix)l_yMy
20 whereas, 0.2 <= x ~= 1.0, 0 <= y <= 0.2 and M = Al or Zr;
b-) Ti2 xZrxV4_yNiy
whereas, 0 ~ x <= 1.5, 0.6 <= y <= 3.5; and
c.) Til-xcrxv2-yNiy
whereas, 0 ~ x <= 0.75, 0.2 <= y <= 1Ø
These active material compositions may also be stated in
atomic percent or dessribed by x-ray diffraction spectra.
We also found that the active materials useful for hydrogen
storage electrodes include a grain phase having means for
reversably storing hydrogen and a primary intergranular
phase having means for catalyzing the hydrogen oxidation
and lower the heat of reaction with hydrogen. Various
devices, including cells and batteries, can be made incor-
porating these active materials. A method of making the
hydrogen storage active materials for use in electrode
includes providing an active material in bulk form wherein
.
_7_ 1Z~9083
the bulk material has means for reversably storing hydrogen
and has a homogeneous phase structure. The method includes
hydriding and dehydriding, and pulverizing the bulk material
to a predetermined particle size distribution.
The preferred embodiment of this invention will
now be described by way of example, with reference to the
drawings accompanying this specification in which:
Figure 1 is a cutaway side view of a flat cell embodi-
ment using an inventive electrode and active material;
Figure 2 is a side view of a jelly-roll cell embodi-
ment using an inventive electrode and active material;
Figure 3 is a graph of representative discharge cur-
rents versus time for an inventive active material of the
first composition group in chunk form;
Figure 4 is a graph of a representative discharge
current versus time for an inventive active material of
the first composition group in electrode form;
Figure 5 is a graph of representative discharge cur-
rents versus time for an inventive active material of the
second composition group in chunk form;
Figure 6 is a graph of representative discharge cur-
rents versus time for an inventive active material of the
third composition group in electrode form;
Figure 7 is a graph of a representative discharge cur-
rent versus time for an inventive active material of thethird composition group in electrode form;
Figure 8 is a scanning electron micrograph of an
inventive active material of the first composition group
before subjecting the material to an inventive process of
preparation;
Figure 9 is a scanning electron micrograph of the
inventive material in Figure 8 after subjecting the
material to the inventive process of preparation; and
.
.
1;2tj9083
-8-
Figure 10 is a graph of the cell capacity versus
cycle life of an inventive electrode incorporating an
inventive active material of the third composition group.
Generally, the present invention provides novel
active materials which reversibly store hydrogen under
conditions which make them exceptionally well-suited for
electrochemical applications. These active materials have
both novel compositions and structures. A first group of
active material compositions incorporate the elements of
titanium, vanadium, and nickel. A second composition
group adds zirconium to the first group of active mate-
rials. A preferred third composition group adds chromium
to the first group of active materials. These materials
may be single or multiphase combinations of amorphous,
microcrystalline, or polycrystalline structures. Pref-
erably, these materials have a multiphase polycrystalline
structure.
The inventive active materials may be prepared by
several methods disclosed herein. A method of reducing
the size or sizing these materials, as well as other
hydride-forming alloys, also is provided. Methods of
fabricating inventive hydrogen storage electrodes from
these active materials are contemplated. The inventive
electrodes are adaptable to assembly as cells with various
configurations such as a jelly-roll or flat configuration.
Electrochemical cells and batteries assembled with the
inventive electrodes provide significantly improved
capacity and cycle life.
In particular, the present invention provides active
materials having three primary groups of compositions
which absorb and store hydrogen and subsequently release
at least a portion of the stored hydrogen to provide a
supply of electrons. Suitable active materials of the
first composition group include titanium present in an
amount greater than about 28 and less than about 36 atomic
, . ~
.
1~ 901~3
g
percent, vanadium present in an amount greater than about
40 and less than about 56 atomic percent, and nickel
present in an amount greater than about 10 and less than
about 22 atomic percent. A preferred active material in
this group includes about 33 atomic percent of titanium,
53 atomic percent of vanadium, and 14 atomic percent of
nickel.
In addition to the above components, the first group
of compositions may also include aluminum and/or zirconium
present in an amount less than about 10 atomic percent.
If one or both of these elements are incorporated, a
preferred amount is about 7 atomic percent of zirconium
and/or about 5 atomic percent of aluminum.
More specifically, the first composition group
includes active materials which are represented by the
cOmposition formula (Tiv2-xNix)l-yMy whereas~ 0-2
x <= 1.0; 0 <= y <= 0.2; and M=Al or Zr. Preferably, y=0
and 0.40 <= x <= 0.45.
The structures of the compositions disclosed herein
were characterized by x-ray diffraction, scanning electron
microscopy, and energy dispersive x-ray analysis. The
types of structure provided by the invention included both
single and multiple phases. An individual phase may have
a structure which is amorphous, microcrystalline, or
polycrystalline (with or without long range order). An
active material with multiple phases may have any com-
bination of these structures. Preferably, the active
materials of all three composition groups have a multi-
phase polycrystalline structure.
In particular, the preferred multiphase polycrystalline
structure of the active materials in the first composition
group includes a grain phase which is a solid solution of
titanium and vanadium with dissolved nickel. The titanium
and vanadium act as hydrogen storage components while the
nickel functions as catalyst and also lowers the heat of
~Z~90~3
--10--
reaction with hydrogen. The composition of this phase
varies from about 20:80 to 30:70 as a ratio of titanium:
vanadium measured in atomic percent. The dissolved nickel
is present in an amount between about 4 to 8 atomic percent.
Between the grain phases of the preferred polycrystal-
line structure is a primary intergranular phase including
a titanium and nickel intermetallic compound with dissolved
vanadium. Such an intermetallic compound exhibits distinct
phases where the constituent atoms are in fixed integral
ratios and is held together by metallic bonding to usually
form a crystal structure. The primary intergranular phase
contains approximately equal amounts of titanium and
nickel, and the dissolved vanadium is present in an amount
between about 6 to 8 atomic percent. This phase functions
as a catalyst for hydrogen oxidation of the primary hydrogen
storage grain phase. The titanium and nickel intermetallic
compound stores less hydrogen than the grain phase and
acts as a channel for hydrogen oxidation. The vanadium
dissolved in the primary intergranular phase increases the
hydrogen storage capacity of this phase and the heat of
reaction with hydrogen.
Several other phases also may be present in these
materials. For example, the grain phase may be at least
partially surrounded by a grain boundary phase which is a
non-equilibrium solid solution of titanium and vanadium
with dissolved nickel. Such a non-equilibrium phase is
not in its lowest energy configuration and may exhibit
concentration gradients within the phase. A composition
of the grain boundary phase is between about 45:55 to
55:45 as a ratio of titanium:vanadium measured in atomic
percent. The dissolved nickel is present in an amount
between about 10 to 14 atomic percent.
Another example is a non-equilibrium phase which
includes Ti2Ni with dissolved vanadium present in an amount
between about 7 to 13 atomic percent. Still another phase
1269(,'~3
ma~ be the vanadium rich side of the titanium and vanadium
binary.
As previously mentioned, the preferred structures of
the three composition groups were characterized by x-ray
diffraction. The major identified peaks of the preferred
polycrystalline structure of the first composition group
occurred at d-spacings of 2.26 angstroms to 2.10 angstroms,
1.55 angstroms to 1.48 angstroms, and 1.27 angstroms to
1.21 angstroms. The primary hydrogen storage grain phase
of the preferred structures is a single phase alloy which
exhibits d-spacings closely corresponding to a vanadium
structure with its lattice parameters shifted due to the
incorporation of varying amounts of other components like
titanium and nickel. Other small peaks of the x-ray spec-
trum may be associated with the intergranular and/or grainboundary phases found in the material. The occurrence of
the peaks in the x-ray diffraction spectrum depends on its
composition and preparation history.
A second composition group contemplated by the present
invention as an active material for an hydrogen storage
electrode includes titanium present in an amount greater
than about 15 and less than about 20 atomic percent,
vanadium present in an amount greater than about 15 and
less than about 40 atomic percent, zirconium present in an
amount greater than about 10 and less than about 20 atomic
percent, and nickel present in an amount greater than
about 30 and less than about 55 atomic percent. Preferably,
a composition includes approximately 17 atomic percent
titanium, 33 atomic percent vanadium, 16 atomic percent
zirconium, and 34 atomic percent nickel. A second pre-
ferred composition includes approximately 17 atomic per-
cent titanium, 20 atomic percent vanadium, 16 atomic
percent zirconium, and 47 atomic percent nickel.
More specifically, the second composition group
includes active materials which are represented by the
1~ 10~3
composition formula Ti2 xZrxV4 yNiy whereas O ~ x <=
1.5 and 0.6 c= y <= 3.5. Preferably, 0.95 <= x <= 1.05
and y = 2 or 3.
The preferred multiphase polycrystalline structure of
the active materials in the second composition group also
includes a grain phase which is an intermetallic compound
of vanadium, titanium, zirconium, and nickel. Again, the
grain phase reversibly stores hydrogen. A composition of
this grain phase is about 26:16:22:36 as a ratio of vanadium:
titanium:zirconium:nickel measured in atomic percent.
Between the grain phases of the preferred polycrystal-
line structure is a primary intergranular phase including
a titanium, zirconium, and nickel intermetallic compound
with dissolved vanadium. A composition of this primary
lS intergranular phase is about 25:20:46 as a ratio of
titanium:zirconium:nickel measured in atomic percent. The
dissolved vanadium is present in an amount of about 9 atomic
percent.
Several other phases also may be present in these
materials. For example, the grain phase may be at least
partially surrounded by a grain boundary phase which is a
non-equilibrium phase incorporating titanium, vanadium,
zirconium, and nickel. A composition of the grain boundary
phase is about 19:20:22:39 as a ratio of titanium:vanadium:
zirconium:nickel as measured in atomic percent.
The x-ray diffraction analysis of the preferred crys-
talline structure of the second composition group identified
peaks at d-spacings of 2.30 angstroms to 2.07 angstroms
and 1.40 angstroms to 1.24 angstroms. Other small peaks
of the x-ray spectrum may be associated with the inter-
granular and~or grain boundary phases found in the mate-
rial. The occurrence of the peaks in the x-ray diffrac-
tion spectrum depends on its composition and preparation
history.
12~90t~3
-13-
A third composition group contemplatsd by the present
invention as an active material for an hydrogen storage
electrode includes titanium present in an amount greater
than about 5 and less than about 25 atomic percent, vanadium
present in an amount qreater than a~out 40 and less than
about 55 atomic percent, chromium present in an amount
greater than about 5 and less than about 25 atomic percent,
and nickel present in an amount greater than about 10 and
less than about 25 atomic percent. Preferably, a composi-
tion would have approximately 17 atomic percent titanium,53 atomic percent vanadium, 17 atomic percent chromium,
and 13 atomic percent nickel.
More specifically, the third composition group includes
active materials which are represented by the composition
15 formula Til_xCrxV2_yNiy whereas, 0 < x ~= 0 75; 0 2 <=
y <= 1Ø Preferably, 0.45 <= x <= 0.55 and 0.4 <= y <=
0.6.
The preferred structure of the active materials in
the third composition group is a multiphase polycrystalline
structure. The active materials include a grain phase
which is a solid solution of titanium, vanadium, and
chromium with dissolved nickel. The titanium, vanadium,
and chromium act as the hydrogen storage components while
the nickel functions as a catalyst and lowers the heat of
reaction with hydrogen. A composition of the grain phase
is between about 60 to 70 atomic percent of vanadium, 20
to 30 atomic percent of chromium, 3 to lO atomic percent
of titanium, and 3 to 10 atomic percent of nicXel.
Between the grains is an intergranular phase including
a titanium, vanadium, and nickel intermetallic compound
with dissolved chromium. The intergranular phase functions
as a hydrogen oxidation catalyst for the utilization of
the primary hydrogen storage grain phase. The intergranular
phase also stores hydrogen, but to significantly lesser
degree than the grain phase. A composition of this phase
, . . .
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~ 9~)83
-14-
is between about 20 to 50 atomic percent of titanium, 40
to 50 atomic percent of nickel, 5 to 20 atomic percent of
vanadium, and 1 to 5 atomic percent of chromium. The
actual composition and the volume fraction of each phase
depends on the thermal history of its preparation and
processing as previously discussed.
The grain phase may be surrounded by a grain boundary
phase which is a solid solution of titanium and vanadium
with dissolved chromium and nickel. A composition and
volume amount of this phase depends on its thermal history
of preparation and processing.
The preferred structures of all three composition
groups may be characterized by a suitable size for the
polycrystalline phases. The grain phase may vary between
about 10 to 100 microns in diameter. The intergranular
phase width may vary between about 1 to 20 microns. The
preferred size of the grain phase is about 25 microns with
an intergranular phase of about 3 microns in width.
The preferred structures for all three composition
groups may be characterized by the volume amounts of the
individual polycrystalline phases. A suitable volume
amount of a grain phase is about 75% to 95% with a primary
intergranular phase present in substantially the remaining
volume amount. A grain boundary phase or other intergranular
phases, if any, would be present in an amount of about 2%.
The volume amounts of the non-equilibrium phases
present in the active material depend on the preparation
of the material. The means of processing as well as the
thermal history of preparing the active material and
fabricating the electrode determine the volume amounts of
any non-equilibrium phase.
The present invention also provides the hydrides of
the active materials in each of the composition groups.
The hydrides of the first composition group preferably
incorporate about 3.8 weight percent of hydrogen. The
.
-15~ 3
hydrides of the second composition group preferably incor-
porate about 1.2 weight percent of hydrogen. The hydrides
of the third composition group preferably incorporate
about 1.4 weight percent of hydrogen.
The x-ray diffraction analysis of the preferred poly-
crystalline structure of the third composition group
identified peaks at d-spacings similar to that found for
the preferred polycrystalline structures of the first
composition group. Likewise, the primary hydrogen storage
grain phase of the preferred structures is a single phase
alloy which exhibits d-spacings closely corresponding to a
vanadium structure with its lattice parameters shifted due
to the incorporation of varying amounts of other components
like titanium, chromium, and nickel.
The present invention contemplates a number of methods
for preparing the above described active materials. Suit-
able methods reproducibly prepare the materials with both
composition and structure that is somewhat homogeneous.
It was found that appropriate amounts of the individual
components of the material could be starting reactants in
a melting process to form a bulk composition or ingot.
Although not limited to a melting process to form the
material, the invention contemplates conventional tech-
niques such as arc-melting and preferably induction melting
for their preparation.
Once the materials were formed in bulk, it became
necessary to reduce the material to a more appropriate
size. Conventional sizing techniques like those pre-
viously mentioned did not prove suitably effective from a
commercial standpoint. Air hammering eventually was
selected, but still was considered commercially unde-
sirable.
It was then discovered that through a novel hydriding
process, the materials could be embrittled, making pulveri-
zation much easier and more economical. The hydriding
sas3
-16-
process includes the steps of hydriding the active material
in bulk form and dehydriding the active material either
before or after pulverizing the material to the appropriate
size. The hydriding step changes the physical form of the
material from a hard, tough ingot into a flaky, ash-like
consistency. This ash-like material is readily pulverized.
The hydriding step includes contacting the bulk
material with hydrogen gas under the appropriate tempera-
ture, pressure, and time conditions to form the hydride of
the material. More specifically, an ingot of the material
may be placed in a reaction vessel. The vessel is subse-
quently sealed and evacuated. Generally, a pressure of
about 10 torr is suitable. The vessel is then pressurized
with hydrogen gas between about 100 to 2000 psi. Generally,
maintaining a partial pressure of hydrogen above about
200 psi for a few minutes is sufficient to form the hydride
at room temperature. These conditions depend on the
composition of the material and its geometry. Materials
that have a slower diffusion rate or low interstitial
mobility for hydrogen will require more time for suitable
embrittlement. The factors that affect the mobility of
hydrogen through the phase regions and of the material's
structure will determine the pressure, time, and tempera-
ture necessary to form a hydride of the material and
effectuate suitable embrittlement.
The vessel may be cooled during the hydriding step to
prevent any temperature increase. The temperature inside
the vessel rises as the material is exposed to the hydrogen
due to the exothermic nature of the hydride formation
reaction (approximately 10 Kcal./mole for these materials).
Without any cooling, the temperature inside the vessel
usually elevates to about 250C. A temperature increase
delays the formation of the hydride. The hydriding reac-
tion spontaneously starts upon exposure to hydrogen gas.
If a barrier or passivation layer forms on the surface of
l;2s~ 3
-17-
the material which prevents contact with the hydrogen gas,
the layer should be removed. For example, if an oxide
layer forms on the material, the hydrogen initially will
slowly penetrate. Initial heating of the material acceler-
ates the hydriding step. Once a portion of the material'ssurface is cleaned of the layer, the hydriding reaction
proceeds rapidly without further assistance.
~ ydride formation of a material batch is ~overned by
the ideal gas law. Sufficient embrittlement for easy size
reduction of some materials does not require complete
hydride formation. For example, with a material such as
Tis3Ni33VI4 which absorbs 2.5 weight percent hydrogen,
it was found that hydriding to at least about 1.5 weight
percent hydrogen provides sufficient embrittlement. Using
the ideal gas law and the amount of hydrogen absorbed for
sufficient embrittlement, the reaction vessel necessary to
embrittle a given batch of material can be readily calculated.
Another step of the novel process is the dehydriding
of the material. Dehydriding the material takes place
after the material has been sufficiently embrittled by
hydride formation. The hydride is returned to the metallic
form of the material.
Specifically, dehydriding includes evacuating the
vessel with the hydride still inside the reaction vessel
and with heating for a sufficient time period to induce
release of the incorporated hydrogen. The material should
be kept at a temperature sufficiently low to avoid changing
the structure of the material. A temperature below 60QC.
is usually suitable. The dehydriding step is more quickly
completed as the temperature increases. Thus, a tempera-
ture of about 400C. is preferred. As the hydrogen is
removed from the vessel it may be compressed and recycled
since it is largely uncontaminated.
After the hydrogen is removed, the material is cooled
to room temperature in an inert environment like argon.
~2~ 3
-18-
The resultant material has the ash-like features of the
hydride and is relatively inert to atmospheric reaction.
Pulverization of the embrittled material may be
accomplished by any conventional device such as mechanical
attritors, jaw crushers, air-hammer, hardened steel mortar
and pestle, or ball-milling. Ball-milling the material
gives a particle size distribution especially useful for
the fabrication of hydrogen storage electrodes. The
particle size of the material may be varied depending upon
the application. The flakes resulting from the embrittle-
ment process are usually about 100 mm. in diameter.
Care must be taken during the pulverization process not to
expose the pulverized material to any conditions which may
allow water or oxygen to contact or react with the pulver-
ized alloy. Using other pulverization techniques willproduce different distributions of particle sizes, as well
as different particle shapes.
It is important, although not critical, that the pul-
verizing step follow the dehydriding step. Several sig-
nificant advantages are demonstrated if the preferredsequence of steps is followed. First, the hydrided form
of the material is very reactive with certain gases like
oxygen which would deleteriously offset the electrochemi-
cal properties of the material. Pulverizing the material
after dehydriding reduces the likelihood of contamination.
This is not critical because the material could be pul-
verized in the hydride form without contamination if care
were taken to provide an inert environment. The complexity
of the procedure, however, makes it less likely to be
economically feasible. Second, a single vessel may be used
to hydride and dehydride the material without transporting
the material between steps. Thus, contamination and
costly handling are avoided.
The novel hydriding process provided herein, may be
in the preparaeion o materials other than the disclosed
. ~
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active material. Other materials suitable for size reduc-
tion with t~le inventive process are ~lydride formers.
The present invention contemplates the fabrication of
an }lydrogen storage electrode from an active material of
the composition or structure previously discussed. The
active material may be sized to an appropriate particle
distribution for preparing the electrodes. Although the
material may be of any convenient particle size, we have
found that the preferred compositions described above
demonstrate the highest electrochemical capacity where the
material has been sized to approximately 38~ or about -400
mesh.
The fabrication of tlle electrodes using the above
described active material may be carried out by several
conventional processes. Preferably, the active materials
were mixed with a binder such as nickel in the amount of
about 7%. Other binders which promote the mechanical
stability of the electrode without deleteriously affecting
its electrochemical properties are suitable. This active
material and binder was then placed in contact with a cur-
rent collector. Although nickel mesh screen was used,
other current collecting means also are suitable.
The material was then pressed to a pressure of about
7 to 10 tons/sq.cm. Various conventional methods for
effectuating the pressure are contemplated by the present
invention.
These materials are then sintered in the range of
800 to 1200C. for a period of several minutes to an
hour. Preferably, a temperature of about 1050C. is used
for about five minutes. As the temperature of the sin-
tering process decreased the length for sintering increased.
It is economically preferred to have a higher sintering
temperature for a shorter period of time.
The present invention also contemplates an electro-
chemical cell which includes at least one electrode means
: -.
i~ 3
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for storing energy. The electrode means is formed from an
active material of the composition or structure prevlously
discussed. The cell also includes at least one counter
electrode means providing for the release of the energy
stored in said electrode means. The counter electrode
means is spaced in operative contact with the electrode
means. The cell also includes a casing which has the
electrode means and the counter electrode means positioned
therein. The counter electrode means includes an electro-
lyte placed in operative contact with the electrode meansand the counter electrode means. A plurality of these
cells may be assembled to produce a hydrogen storage
battery.
Various electrochemical cell embodiments utilizing
the inventive active material compositions are contemplated.
Referring to Figure 1, a flat cell lO is illustrated which
uses at least one substantially flat plate 15 incorporating
the active material described above. Interleaved between
the active material is a current collector 20 which is in
electrical contact with the active material and a tab 25.
The collector 20 and tab 25 may be made of suitably con-
ductive metals such as nickel. The flat cell 10 includes
a counter electrode 30 which is substantially flat and
aligned to be in operative contact with plate 15. A
separator 35 is disposed between the counter electrode 30
and the plate 15.
A second substantially flat plate 40 may be spaced in
operative contact with the counter electrode 30 on the
side opposite the first plate 15. Similarly interleaved
between the active material is a current collector 45
which is in electrical contact with the active material
and the tab 50. A second separator 55 is disposed between
the second plate 40 to electrically contact the tab 50 and
the counter electrode 30.
'' '
~,
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~ 90~3
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The cell lO depicted in Figure l may be sealed ir~ a
suitable material, such as a plastic wrap 60, which does
not deteriorate in contact with the electrolyte used and
allows venting of the cell 10 should it gas during opera-
tion. The first and second tabs 25, 50 are electricallycomlected to first set of leads 65 which extends outside
of the cell plastic 60. Likewise, a second lead 70 elec-
trically connects to the counter electrode 30 and extends
outside of the cell plastic 60.
Figure 2 illustrates a commercially preferred jelly-roll
cell lOO which is made by spirally winding a flat cell
about an axis 105. The jelly-roll cell may then be placed
in a can which contains a conductive electrolyte (not
shown) which contacts the tabs llO interleaved with the
plate 115 of the material described above. A separator
120 is spaced between the sheets 115 and a counter elec-
trode 125.
EXAMPLE 1
A first group of compositions represented by the
formula (TiV2_XNix)l_yMy whereas, 0.2 <= x <= l.O; O <=
y <= 0.2; and M=A1 or Zr. Compositions having these
specific formulae presented in Table 1 were prepared by
weighing and mixing powders of the individual components
each having a purity in excess of 99.7%. Each mixture was
pressed into a pellet and melted by induction melting in
an argon atmosphere. The ingot was cooled by an ice bath
and then crushed with an air hammer. Chunk samples ranging
up to 1.0 mm. in length and 250 mg. in weight were chosen
for electrochemical testing.
Each chunk sample of a composition was squeeze wrapped
by a pure nickel screen basket about 1 cm. 2 and placed in
a 4M KOH solution with a platinum counter electrode and an
Hg/HgO reference electrode. The open circuit voltage was
about -.970 volt vs. Hg/HgO the electrochemical capacity
.' : '
: - - . ,
tV~3
-22-
of each composition measured at a 50 mA/g disc~large rate
is represented in Table 1.
TABLE 1
ELECTROCHEMICAL CAPACITY OF (TiV2 XNix)l yMy
AT 50 mA/g DISCHARGE RATE
MATERIAL
(Atomic Percent) CAPACITY (mAh/g)
Vs3Ti33Nil4
V4 7Ti 3 3Ni 2 0 310
10 Vs o . 8Ti 3 1 . ,Ni l 2 . 7Al4. 8 328
V4 9 . sTi 3 3Ni 1 2 4Als-1 400
Figure 3 demonstrates the discharge rate capability
of Vs3Ti33Nil4 material from this group in chunk form at
representative discharge rates versus time.
A powder sample of a Vs3Ti33Nil4 was provided by sub-
jecting the composition to an air hammer to achieve a -400
mesh (equivalent to approximately 38 micron diameter
particle size). The powder was positioned over a pure
nickel grid and pressed to 7 tons/sq.cm. Subsequently,
the electrode was sintered at 825C. for one hour. The
electrochemical capacity of each powder composition was
measured in a 4M KOH solution with a platinum counter
electrode and an Hg/HgO reference electrode. The elec-
trochemical capacity was measured at a discharge rate of
25 50 mA/g and the discharge rate capability of Vs3Ti33Nil4
at representative discharge rates versus time in Figure 4.
The cycle life of the first group of compositions was
measured by testing certain representative compositions as
either a chunk sample or a powder sample. For instance, a
30 chunk sample of Vs3Ti33Nil4 cycled for more than 10 cycles
in 4M KOH at a charge rate of 100 mA/g for 6 hours and a
discharge rate of 100 mA/g to -.700 volt vs. Hg/HgO refer-
ence electrode. No significant degradation was observed.
-23- lZ ~9 ~ 83
EXAMPLE 2
~ A second group of compositions represented by the
formula Ti2 xZrxV4 yNiy whereas O ~ x ~= 1.5; 0.6 <=
y <= 3.5. Compositions having the specific formulae
presented in Table 2 were prepared by weighing and mixing
powders of the individual components each having a purity
in excess of 99.5%. Each mixture was pressed into a
pellet and melted by induction melting in an argon
atmosphere. The ingot was cooled by an ice bath and then
crushed with an air hammer. Chunk samples ranging up to
1.0 mm. thick and 300 mg. in weight were chosen for elec-
trochemical testing.
A chunk sample of each composition was squeeze wrapped
by a pure nickel screen basket about 1 cm. 2 and placed in
a 4M KOH solution with a platinum counter electrode and an
Hg/HgO reference electrode. The open circuit voltage was
about -.970 volts vs. Hg~HgO. The electrochemical capacity
of each composition was measured at 50 mA/g discharge rate
is represented in Table 2.
TABLE 2
ELECTROCHEMICAL CAPACITY OF Ti2 xZrxV4 yNiy
AT 50 mA/g DISCHARGE RATE
MATERIAL
(Atomic Percent) CAPACITY (mAh/g)
Ti~7V,7ZrlsNisO ` 240
Til7V20Zrl6Ni47 310
Til7V2szrl6Ni42 265
Til7V33Zrl~Ni34 320
Figure 5 demonstrates the discharge rate capability
of a sample material from this group in chunk form at
representative discharge rates versus time.
The cycle life of this third Qroup of compositions
was measured by testing a representative composition as a
~: . ' . .
. ' - .
~ ;90~3
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chunk sample. Particularly, the composition Til7V33Zr,6Ni34
completed more than 120 cycles in 4M KOH at a charge rate
of 200 mA/g for 3 hours and a discharge rate of 100 mA/g
to -.720 volt vs. Hg/HgO reference electrode. No signifi-
cant degradation was observed.
EXAMPLE 3
A third group of compositions represented by the
formula Til xCrxV2 yNiy whereas O < x <= 0.75 and 0.2 <=
y <= 1Ø Three compositions having the specific formulae
presented in Table 3 were prepared by weighing and mixing
powders of the individual components each having a purity
in excess of 99.5%. Each mixture was pressed into a
pellet and melted by induction melting in an argon atmosphere.
The ingot was cooled by an ice bath and then crushed with
an air hammer. Chunk samples ranging up to 1.0 mm thick
and 300 mg. in weight were chosen for electrochemical
testing .
A chunk sample of each composition was squeeze wrapped
by a pure nickel screen basket about lcm. 2 and placed in a
4M KOH solution with a platinum counter electrode and an
Hg/HgO reference electrode. The open circuit voltage was
about -.970 volt vs. Hg/HgO. The electrochemical capacity
of each composition measured at a 50 mA/g discharge rate
is represented in Table 3.
TABLE 3
ELECTROCHEMICAL CAPACITY OF Til xCrxV2 yNiy
AT 50 mA/g DISCHARGE RATE
MATERIAL
(Atomic Percent) CAPACITY (mAh/g~
Ti2DCrl3Vs4Nil3 300
Ti,7Crl7Vs3Nil3 350
Ti 2 s Cr~V4 7Ni 2 o 260
30~3
.
-25-
Ti ~Cr2 5V4 7Ni 2 ~ 200
Til6Crl~V47Ni2l 280
Figure 6 demonstrates the discharge rate capability
of a sample material from this group in chunk form at
representative discharge rates versus time.
A powder sample of a Ti~7Crl7Vs3Ni~3 was provided by
subjecting the composition to an air hammer to achieve a
-400 mesh. The powder was positioned over a pure nickel
grid and pressed to 10 tons/sq.cm. Subsequently, the
electrode was sintered at 1050C. for 5 minutes. The
electrochemical capacity of each powder composition was
measured in a 4M KOH solution with a platinum counter
electrode and an Hg/HgO reference electrode. The electro-
chemical capacity was measured at a discharge rate of
50 mA/g and the discharge rate capability at representa-
tive discharge rates versus time in Figure 7.
The cycle life of this second group of compositions
was measured by compositions as both a chunk sample and a
powder sample. For instance, a chunk sample of
Til,Crl7Vs3Nil3 cycled for more than 150 cycles in 4M ~OH
at a charge rate of 100 mA/g for 6 hours and a discharge
rate of 100 mA/g to -.720 volt vs. Hg/HgO reference elec-
trode. No significant degradation was observed.
EXAMPLE 4
An ingot of a Ti33Ni~4Vs3 material was made by weigh-
ing out respective amounts of the elemental metals, melt-
ing them together, and allowing it to cool to room tempera-
ture. Two hundred grams of the material was placed into a
reaction vessel with an interior volume of about 1 liter.
The vessel was leak tight to both vacuum and pressurized
gas. The vessel was evacuated to 10 3 torr and pressurized
to about 600 psi. with commercial grade hydrogen gas. The
material was allowed to stand for about 10 hours. Without
90~3
-26-
breaking the seal, the hydrogen gas was removed. The
vessel was heated to 400C. for several hours until the
hydrogen pressure coming out of the vessel was negligible.
Argon was introduced and the reactor was allowed to cool
to room temperature. After the seal was broken, the ingot
was observed to have been reduced to flakes and powders of
an ash-like consistency.
Scanning electron micrographs were taken before
hydriding in Figure 8 and after hydriding in Figure 9.
These micrographs dramatically show cracking of the mate-
rial around the various phase regions. Yet, the structure
of the material remains unchanged.
The flakes were then pulverized using a ball-mill for
three hours yielding the following distribution: greater
than 38 micron size 25.4%; 30 to 38 micron size 12.5%; 5
to 30 micron size 60.4%; and 5 micron size or less 1.8%.
Material which was greater than 38 micron size were subse-
quently reduced by longer ball-milling.
The 38 micron size particles then mixed with a nickel
binder and pressed onto a conductive substrate of pure
nickel mesh. The material filled mesh was then used as a
hydrogen storage anode in a half-cell. This material
showed an excellent electrochemical performance, equivalent
to the material that had been air-hammered.
EXAMPLE 5
An active material composition of the formula
V53Ti,7Cr~Ni,~ was prepared in accordance with the proce-
dure listed in Example 3. The active material was then
hydrided as in Example 4 and reduced to size of about
-200 mesh. A nickel binder was added to the active material
in an amount of about 7 atomic percent. After pressing,
the active material was sintered at 1050C. for five
minutes in an hydrogen/argon atmosphere.
.
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A standard sub C size cell was fabricated with a
Pellon separator using a 1.8 Ahr. positive electrode
produced by Eagle-Picher. A 30% KOH electrolyte was added
and the cell was cycled by charging at 300mA. for 8 hours.
The initial capacity of the cell was approximately 1.7 Ahr.
with a 1.0 volt cutoff. The capacity has maintained itself
at approximately 1.7 Ahr. even after 170 cycles. Absolutely
no degradation in the capacity has been observed. Eigure 10
illustrates the cycling regimen for this electrode demon-
strating its long cycle life with a sustained capacity.
The present invention demonstrates a new and improvedelectrode, cell, and battery fabricated with novel active
materials. The cells demonstrate bulk hydrogen storage
with commercially acceptable charge and discharge rates,
deep discharge capability, and long cycle life. The
mechanical integrity of electrodes made with the inventive
materials promotes long cycle life for the cells without
substantial structural change or poisoning. The improved
electrochemical performance and structural stability of
the inventive electrodes is further benefited by economical
fabrication. The ease and simplicity of their fabrication
is demonstrated by the embrittlement process.
Modifications and variations of the present invention
are possible in light of the above teachings. It is,
therefore, to be understood that within the scope of the
appended claims the invention may be practiced otherwise
than as specifically described.
