U.S. patent application number 15/674667 was filed with the patent office on 2017-11-30 for activation of laves phase-related bcc metal hydride alloys for electrochemical applications.
The applicant listed for this patent is Ovonic Battery Company, Inc.. Invention is credited to Baoquan Huang, Taihei Ouchi, Kwo-hsiung Young.
Application Number | 20170346086 15/674667 |
Document ID | / |
Family ID | 55167428 |
Filed Date | 2017-11-30 |
United States Patent
Application |
20170346086 |
Kind Code |
A1 |
Young; Kwo-hsiung ; et
al. |
November 30, 2017 |
ACTIVATION OF LAVES PHASE-RELATED BCC METAL HYDRIDE ALLOYS FOR
ELECTROCHEMICAL APPLICATIONS
Abstract
Laves phase-related BCC metal hydride alloys historically have
limited electrochemical capabilities. Laves phase-related BCC metal
hydride alloys are provided herein with greater than 200 mAh/g
capacities and commonly at or greater than 400 mAh/g capacities. By
decreasing the temperature or increasing the hydrogen pressure the
phase structure of the material a synergistic effect between
multiple phases in the resulting alloy is achieved thereby greatly
improving the electrochemical capacities.
Inventors: |
Young; Kwo-hsiung; (Troy,
MI) ; Ouchi; Taihei; (Oakland Township, MI) ;
Huang; Baoquan; (Troy, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ovonic Battery Company, Inc. |
Rochester Hills |
MI |
US |
|
|
Family ID: |
55167428 |
Appl. No.: |
15/674667 |
Filed: |
August 11, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14340913 |
Jul 25, 2014 |
9768445 |
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15674667 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/383 20130101;
C01P 2004/03 20130101; Y02E 60/128 20130101; C01P 2006/40 20130101;
H01M 4/242 20130101; C01B 3/0031 20130101; C01B 6/24 20130101; H01M
12/08 20130101; C01P 2002/72 20130101; H01M 10/30 20130101; H01M
2004/027 20130101; Y02E 60/327 20130101; Y02E 60/10 20130101; Y02E
60/32 20130101 |
International
Class: |
H01M 4/38 20060101
H01M004/38; C01B 3/00 20060101 C01B003/00; C01B 6/24 20060101
C01B006/24 |
Claims
1. An activated mixed BCC and Laves phase metal hydride alloy
comprising the composition of Formula I:
Ti.sub.wV.sub.xCr.sub.yM.sub.z (I) where w+x+y+z=1,
0.1.ltoreq.w.ltoreq.0.6, 0.1.ltoreq.x.ltoreq.0.6,
0.01.ltoreq.y.ltoreq.0.6, and M is selected from the group
consisting of B, Al, Si, Sn and transition metals, said alloy
having a capacity in excess of 400 milliampere hours per gram at
cycle 10.
2. The alloy of claim 1, wherein the alloy is predominantly a
combination of BCC phase and Laves phase, said BCC phase in a phase
abundance of greater than 5 weight % and less than 95 weight %,
said Laves phase in abundance of greater than 5 weight % and less
than 95 weight %.
3. The alloy of claim 1 comprising a BCC phase crystallite size of
less than 400 angstroms.
4. The alloy of claim 1 having a capacity in excess of 420
milliampere hours per gram.
5. The alloy of claim 1 comprising Formula II:
Ti.sub.0.4+x/6Zr.sub.0.6-x/6Mn.sub.0.44Ni.sub.1.0Al.sub.0.02Co.sub.0.09(V-
Cr.sub.0.3Fe.sub.0.063).sub.x (II) where x is 0.7 to 2.8.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/340,913 filed Jul. 25, 2014, the entire
contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to alloy materials and methods for
their fabrication. In particular, the invention relates to metal
hydride alloy materials that are capable of absorbing and desorbing
hydrogen. Methods of activating BCC metal hydride alloys are
provided that produce high capacity for use in electrochemical
applications.
BACKGROUND OF THE INVENTION
[0003] Certain metal hydride (MH) alloy materials are capable of
absorbing and desorbing hydrogen. These materials can be used as
hydrogen storage media, and/or as electrode materials for fuel
cells and metal hydride batteries including nickel/metal hydride
(Ni/MH) and metal hydride/air battery systems.
[0004] When an electrical potential is applied between the cathode
and a MH anode in a MH cell, the negative electrode material (M) is
charged by the electrochemical absorption of hydrogen to form a
metal hydride (MH) and the electrochemical evolution of a hydroxyl
ion. Upon discharge, the stored hydrogen is released to form a
water molecule and evolve an electron. The reactions that take
place at the positive electrode of a nickel MH cell are also
reversible. Most MH cells use a nickel hydroxide positive
electrode. The following charge and discharge reactions take place
at a nickel hydroxide positive electrode.
##STR00001##
[0005] In a MH cell having a nickel hydroxide positive electrode
and a hydrogen storage negative electrode, the electrodes are
typically separated by a non-woven, felted, nylon or polypropylene
separator. The electrolyte is usually an alkaline aqueous
electrolyte, for example, 20 to 45 weight percent potassium
hydroxide.
[0006] One particular group of MH materials having utility in MH
battery systems is known as the AB.sub.x class of material with
reference to the crystalline sites occupied by its member component
elements. AB.sub.x type materials are disclosed, for example, in
U.S. Pat. No. 5,536,591 and U.S. Pat. No. 6,210,498. Such materials
may include, but are not limited to, modified LaNi.sub.5 type
(AB.sub.5) as well as the Laves-phase based active materials
(AB.sub.2). These materials reversibly form hydrides in order to
store hydrogen. Such materials utilize a generic Ti--Zr--Ni
composition, where at least Ti, Zr, and Ni are present with at
least one or more of Cr, Mn, Co, V, and Al. The materials are
multiphase materials, which may contain, but are not limited to,
one or more Laves phase crystal structures.
[0007] Other AB.sub.x materials include the Laves phase-related
body centered cubic (BCC) materials that are a family of MH alloys
with a two-phase microstructure including a BCC phase and a Laves
phase historically present as C14 as an example. These materials
exhibit high density of the phase boundaries that allow the
combination of higher hydrogen storage capacity of BCC and good
hydrogen absorption kinetics and relatively high surface catalytic
activity of the C14 phase. Many studies have been undertaken to
optimize these materials. Young et al., Int. J. Hydrogen Energy,
http://dx.doi.org/10.1016/j.ijhydene.2014.01.134 (article in press)
describes a systematic study of these materials with a broad range
of BCC/C14 ratio. These results reveal that while these materials
have many desirable properties, the electrochemical storage
capacity produced by these materials does not exceed 175 mAh/g.
[0008] Prior AB.sub.5 MH materials suffer from insufficient
hydrogen-absorbing capabilities which equates to low energy
density. This has made increasing the capacity of systems employing
these materials exceedingly difficult. On the other hand, AB.sub.2
alloys commonly suffer from high cost and low high-rate
performance.
[0009] Rare earth (RE) magnesium-based AB.sub.3- or
A.sub.2B.sub.7-types of MH alloys are promising candidates to
replace the currently used AB.sub.5 MH alloys as negative
electrodes in Ni/MH batteries due in part to their higher
capacities. While most of the RE-Mg-Ni MH alloys were based on
La-only as the rare earth metal, some Nd-only A.sub.2B.sub.7
(AB.sub.3) alloys have recently been reported. In these materials,
the AB.sub.3.5 stoichiometry is considered to provide the best
overall balance among storage capacity, activation, high-rate
dischargeability (HRD), charge retention, and cycle stability. The
pressure-concentration-temperature (PCT) isotherm of one Nd-only
A.sub.2B.sub.7 alloy showed a very sharp take-off angle at the
a-phase [K. Young, et al., Alloys Compd. 2010; 506: 831] which can
maintain a relatively high voltage during a low state-of-charge
condition. Compared to commercially available AB.sub.5 MH alloys, a
Nd-only A.sub.2B.sub.7 exhibited a higher positive electrode
utilization rate and less resistance increase during a 60.degree.
C. storage, but also suffered higher capacity degradation during
cycling [K. Young, et al., Int. J. Hydrogen Energy, 2012; 37:9882].
Another issue with known A.sub.2B.sub.7 alloys is that they suffer
from inferior HRD relative to the prior AB.sub.5 alloy systems.
[0010] As such, there is a need for improved hydrogen storage
materials and processes of their manufacture or activation. As will
be explained herein below, the present invention addresses these
needs by proving Laves phase-related BCC metal hydride alloys that
for the first time exhibit greatly improved electrochemical
properties. These and other advantages of the invention will be
apparent from the drawings, discussion, and description which
follow.
SUMMARY OF THE INVENTION
[0011] The following summary of the invention is provided to
facilitate an understanding of some of the innovative features
unique to the present invention and is not intended to be a full
description. A full appreciation of the various aspects of the
invention can be gained by taking the entire specification, claims,
drawings, and abstract as a whole.
[0012] Addressing the needs of providing stable high capacity
nickel metal hydride battery systems is desirable. Provided are
processes that are useful for generating increased stable capacity
relative to prior methods. As such, a process for activating a
Laves phase-related BCC metal hydride alloy of Formula I:
Ti.sub.wV.sub.xCr.sub.yM.sub.z (I)
where w+x+y+z=1, 0.1.ltoreq.w.ltoreq.0.6, 0.1.ltoreq.x.ltoreq.0.6,
0.01.ltoreq.y.ltoreq.0.6, and M is selected from the group
consisting of B, Al, Si, Sn and transition metals, where the
process includes: subjecting the laves phase-related BCC metal
hydride alloy to an atmosphere comprising hydrogen at a
hydrogenation pressure; and cooling the alloy during the step of
subjecting to produce an activated metal hydride alloy having a
capacity in excess of 200 milliamperes per gram--a level not
achieved by prior activation processes. In some embodiments, the
step of cooling is at a maximum activation temperature of 300
degrees Celsius or less. The atmosphere is at a hydrogenation
pressure that is optionally 1.4 megapascals or greater, optionally
6 megapascals or greater. The processes produce an activated metal
hydride alloy optionally having a capacity of 300 milliamperes per
gram or greater, optionally 350 milliamperes per gram or greater.
In some embodiments the activated metal hydride alloy has less than
24% C14 phase. In some embodiments, the activated metal hydride
alloy is predominantly a combination of BCC phase and Laves phase,
said BCC phase in abundance of greater than 5% and less than 95%,
the Laves phase in abundance of greater than 5% and less than 95%.
Optionally, the activated metal hydride alloy includes a BCC phase
crystallite size of less than 400 angstroms. In any of the
foregoing or combinations thereof the laves phase-related BCC metal
hydride alloy is optionally of Formula II:
Ti.sub.0.4+x/6Zr.sub.0.6-x/6Mn.sub.0.44Ni.sub.1.0Al.sub.0.02Co.sub.0.09(-
VCr.sub.0.3Fe.sub.0.063).sub.x (II)
where x is 0.7 to 2.8.
[0013] Also provided are activated alloys having excellent capacity
far superior to other alloys of like elemental composition where
the capacity is at or in excess of 200 milliamperes per gram,
optionally in excess of 300 milliamperes per gram. The activated
alloy is defined by Formula I:
Ti.sub.wV.sub.xCr.sub.yM.sub.z (I)
[0014] where w+x+y+z=1, 0.1.ltoreq.w.ltoreq.0.6,
0.1.ltoreq.x.ltoreq.0.6, 0.01.ltoreq.y.ltoreq.0.6 and M is selected
from the group consisting of B, Al, Si, Sn and transition metals.
Optionally, the alloy includes predominantly a combination of BCC
phase and Laves phase, said BCC phase in abundance of greater than
5% and less than 95%, said Laves phase in abundance of greater than
5% and less than 95%. Optionally the alloy includes a BCC phase
crystallite size of less than 400 angstroms. In some embodiments,
the alloys comprises a material of Formula II:
Ti.sub.0.4+x/6Zr.sub.0.6-x/6Mn.sub.0.44Ni.sub.1.0Al.sub.0.02Co.sub.0.09(-
VCr.sub.0.3Fe.sub.0.063).sub.x (II)
where x is 0.7 to 2.8.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates alloy phase distribution as observed in
an SEM image of a hydrogen storage alloy prior to activation;
[0016] FIG. 2 illustrates the microstructure of hydrogen storage
alloys activated to provide improved electrochemical properties and
illustrating two predominant phases, C14 and BCC;
[0017] FIG. 3 illustrates the FWHM of the BCC (110) peak from
control and hydrogen storage alloys activated to provide improved
electrochemical properties and demonstrating the reduced
crystallite size of the alloys activated by exemplary processes as
described herein;
[0018] FIG. 4 illustrates gaseous phase hydrogen storage
characteristics of various alloy materials formed by exemplary
processes as described herein.
BRIEF DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0019] The following description of particular embodiment(s) is
merely exemplary in nature and is in no way intended to limit the
scope of the invention, its application, or uses, which may, of
course, vary. The invention is described with relation to the
non-limiting definitions and terminology included herein. These
definitions and terminology are not designed to function as a
limitation on the scope or practice of the invention but are
presented for illustrative and descriptive purposes only. While the
processes or compositions are described as an order of individual
steps or using specific materials, it is appreciated that steps or
materials may be interchangeable such that the description of the
invention may include multiple parts or steps arranged in many ways
as is readily appreciated by one of skill in the art.
[0020] It will be understood that when an element is referred to as
being "on" another element, it can be directly on the other element
or intervening elements may be present therebetween. In contrast,
when an element is referred to as being "directly on" another
element, there are no intervening elements present.
[0021] It will be understood that, although the terms "first,"
"second," "third" etc. may be used herein to describe various
elements, components, regions, layers, and/or sections, these
elements, components, regions, layers, and/or sections should not
be limited by these terms. These terms are only used to distinguish
one element, component, region, layer, or section from another
element, component, region, layer, or section. Thus, "a first
element," "component," "region," "layer," or "section" discussed
below could be termed a second (or other) element, component,
region, layer, or section without departing from the teachings
herein.
[0022] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting. As
used herein, the singular forms "a," "an," and "the" are intended
to include the plural forms, including "at least one," unless the
content clearly indicates otherwise. "Or" means "and/or." As used
herein, the term "and/or" includes any and all combinations of one
or more of the associated listed items. It will be further
understood that the terms "comprises" and/or "comprising," or
"includes" and/or "including" when used in this specification,
specify the presence of stated features, regions, integers, steps,
operations, elements, and/or components, but do not preclude the
presence or addition of one or more other features, regions,
integers, steps, operations, elements, components, and/or groups
thereof. The term "or a combination thereof" means a combination
including at least one of the foregoing elements.
[0023] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
disclosure belongs. It will be further understood that terms such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0024] Historical hydrogen storage alloys having Laves
phase-related BCC structures have been studied for some time to
identify how to promote a synergistic effect between the C14 and
BCC phases of the system. Prior studies substituting A-site and
B-site elements have been performed on numerous mixed phase alloys
some of which were found to increase or decrease C14 phase
abundance. Compositional refinements have continued as a way to
improve both the gaseous and electrochemical hydrogen storage
properties of these alloys. While these efforts met with some
success and often mixed conclusions, achieving capacities in excess
of 200 mAh/g remained elusive. The processes provided herein
represent a simple and elegant solution to these problems by
producing activated hydrogen storage alloys of the Laves-phase
related BCC structured materials that exhibit excellent
electrochemical properties. The processes can be used to either
reduce or limit the amount of C14 phase, increase the relative
amount of BCC phase to improve the hydrogen storage capacity, or
both. Alloys produced by these methods are also provided.
[0025] Provided are hydrogen storage alloys having a Laves
phase-related BCC structure that exhibit excellent electrochemical
properties unexpectedly superior to prior materials of similar
composition. A Laves-phase related BCC metal hydride alloy of the
composition of Formula I is provided.
Ti.sub.wV.sub.xCr.sub.yM.sub.z (I)
where w+x+y+z=1, 0.1.ltoreq.w.ltoreq.0.6, 0.1.ltoreq.x.ltoreq.0.6,
0.01.ltoreq.y.ltoreq.0.6 and M is selected from the group
consisting of B, Al, Si, Sn and one or more transition metals. The
alloy is activated by particular processes to promote formation of
increased BCC phase and limit AB.sub.2 phase in the resulting
materials. The result is an activated metal hydride alloy having
improved electrochemical properties including a capacity at or in
excess of 200 mAh/g.
[0026] Optionally, a Laves-phase related BCC metal hydride alloy of
the composition of Formula II:
Ti.sub.0.4+x/6Zr.sub.0.6-x/6Mn.sub.0.44Ni.sub.1.0Al.sub.0.02Co.sub.0.09(-
VCr.sub.0.3Fe.sub.0.063).sub.x (II)
where x is 0.7 to 2.8.
[0027] In some embodiments, an activated metal hydride alloy
includes a capacity well in excess of 200 mAh/g, optionally 220
mAh/g, 240 mAh/g, 260 mAh/g, 280 mAh/g, 300 mAh/g, 310 mAh/g, 320
mAh/g, 330 mAh/g, 340 mAh/g, 350 mAh/g, 360 mAh/g, 370 mAh/g, or
more. Optionally, an activated metal hydride alloy includes a
capacity between 200 and 400 mAh/g. Optionally, an activated metal
hydride alloy includes a capacity between 300 and 400 mAh/g.
Optionally, an activated metal hydride alloy includes a capacity
between 300 and 380 mAh/g.
[0028] The physical structure of the material along with its
composition and lack of oxidation relative to prior alloy materials
of similar chemical composition promote the excellent
electrochemical properties of the activated metal hydride alloy. An
activated metal hydride alloy optionally is predominantly formed of
BCC phase and Laves phase structure. Without being limited to one
particular theory, it is believed that the predominance of the
structure being in the BCC phase and Laves phase increases a
synergistic effect produced by the presence of the two phases. As
such, the activated metal hydride alloy produced by the processes
as disclosed herein optionally have BCC phase in abundance of
greater than 5% and less than 95%, a Laves phase in abundance of
greater than 5% and less than 95% with the combination of BCC phase
and Laves phase being in excess of 50% of the material structure.
Optionally, the BCC phase is at or between 10% and 95%, 20% and
95%, 30% and 95%, 40% and 95%, 50% and 95%, 60% and 95%, 70% and
95%, or 80% and 95%, optionally also in any such instance with a
Laves phase in excess of 5%. Optionally, the Laves phase is at or
between 10% and 95%, 20% and 95%, 30% and 95%, 40% and 95%, 50% and
95%, 60% and 95%, 70% and 95%, or 80% and 95%, optionally also in
any such instance with a BCC phase in excess of 5%. In some
embodiments, composition has a C14 Laves phase that is less than
30%, optionally less than 25%, optionally less than 20%, optionally
less than 15%, optionally less than 14%, optionally, less than 13%,
optionally less than 12%.
[0029] The activated hydrogen storage alloy is provided with a
crystallite size of the BCC phase that is sufficiently small to
promote the electrochemical properties. The alloys produced by the
presently described process have a BCC crystallite size of 400
.ANG. or less, optionally 390 .ANG. or less, optionally 380 .ANG.
or less, optionally 370 .ANG. or less, optionally 360 .ANG. or
less, optionally 350 .ANG. or less, optionally 340 .ANG. or less,
optionally 330 .ANG. or less, optionally 320 .ANG. or less,
optionally 310 .ANG. or less, optionally 300 .ANG. or less,
optionally 290 .ANG. or less, optionally 280 .ANG. or less,
optionally 270 .ANG. or less, optionally 260 .ANG. or less,
optionally 250 .ANG. or less, optionally 240 .ANG. or less,
optionally 230 .ANG. or less, optionally 220 .ANG. or less,
optionally 210 .ANG. or less, optionally 200 .ANG. or less.
Optionally, the crystallite size of the BCC phase is from 200 .ANG.
to 300 .ANG..
[0030] The physical, structural, and electrochemical properties of
the active hydrogen storage alloy are created by new methods
described herein of hydriding the base materials to prevent too
much Laves phase from forming in the material, increase the amount
of BCC phase structure to the material, or combinations thereof. As
such, processes of activating (hydriding) a Laves phase-related BCC
metal hydride alloy of Formula I or Formula II are provided. A
process includes subjecting the Laves phase-related BCC metal
hydride alloy to an atmosphere including hydrogen at a
hydrogenation pressure and simultaneously cooling the alloy to
produce an activated metal hydride alloy having a capacity in
excess of 200 mA/g. Subjecting a Laves phase-related BCC metal
hydride alloy to hydrogen at elevated pressures will increase the
temperature of the material due to the exothermic nature of the
hydride formation reaction. It was discovered that allowing the
temperature of the alloy to increase in an uncontrolled manner is
detrimental to the resulting electrochemical properties of the
activated alloy. As such, the processes include an active cooling
step. Without being limited one particular theory, controlling the
temperature of the material during hydriding promotes excess
AB.sub.2 phase structure from forming in the alloy during
activation. Temperature control is achieved by cooling the reaction
vessel such as with a water jacketed system or bath, or by other
methods known in the art. Optionally, the reaction temperature of
the alloy does not exceed 300.degree. C.
[0031] In some embodiments, the temperature of the alloy is
maintained between room temperature and optionally 300.degree. C.,
optionally 295.degree. C., optionally 290.degree. C., optionally
285.degree. C., optionally 280.degree. C., optionally 275.degree.
C., optionally 270.degree. C., optionally 260.degree. C.,
optionally 250.degree. C., optionally 240.degree. C., optionally
230.degree. C., optionally 220.degree. C., optionally 210.degree.
C., optionally 200.degree. C., optionally 190.degree. C.,
optionally 180.degree. C., optionally 170.degree. C., optionally
160.degree. C., optionally 150.degree. C., optionally 140.degree.
C., optionally 130.degree. C., optionally 120.degree. C.,
optionally 110.degree. C., optionally 100.degree. C., optionally
90.degree. C., optionally 80.degree. C., optionally 70.degree. C.,
optionally 60.degree. C., optionally 50.degree. C., optionally
40.degree. C., optionally 30.degree. C. In some embodiments, an
alloy is maintained during activation to a temperature between room
temperature and 300.degree. C., or to any value or range
therebetween.
[0032] Increasing hydrogen pressure was also discovered to be
useful to promote formation of increased amounts of BCC phase in
the resulting activated hydrogen storage alloy. As such, a process
optionally includes activating the Laves phase-related BCC metal
hydride alloy at a hydrogenation pressure of 1.4 MPa or greater,
optionally 1.5 MPa or greater, optionally 1.8 MPa or greater,
optionally 2 MPa or greater, optionally 3 MPa or greater,
optionally 4 MPa or greater, optionally 5 MPa or greater,
optionally 6 MPa or greater.
[0033] In some embodiments, both a hydrogenation pressure in excess
of 1.4 MPa is combined with controlling the temperature to
300.degree. C. or less. As such, a process optionally includes
activating an alloy with a hydrogenation pressure of between 1.4
MPa to 6 MPa, or greater, with cooling to prevent the alloy from
exceeding 300.degree. C., optionally 295.degree. C., optionally
290.degree. C., optionally 285.degree. C., optionally 280.degree.
C., optionally 275.degree. C., optionally 270.degree. C.,
optionally 260.degree. C., optionally 250.degree. C., optionally
240.degree. C., optionally 230.degree. C., optionally 220.degree.
C., optionally 210.degree. C., optionally 200.degree. C.,
optionally 190.degree. C., optionally 180.degree. C., optionally
170.degree. C., optionally 160.degree. C., optionally 150.degree.
C., optionally 140.degree. C., optionally 130.degree. C.,
optionally 120.degree. C., optionally 110.degree. C., optionally
100.degree. C., optionally 90.degree. C., optionally 80.degree. C.,
optionally 70.degree. C., optionally 60.degree. C., optionally
50.degree. C., optionally 40.degree. C., optionally 30.degree. C.
At any one of the above temperature ranges the hydrogenation
pressure is optionally between 6 MPa and optionally 1.4 MPa,
optionally 1.5 MPa, optionally 1.6 MPa, optionally 1.7 MPa,
optionally 1.8 MPa, optionally 1.9 MPa, optionally 2 MPa,
optionally 2.1 MPa, optionally 2.2 MPa, optionally 2.3 MPa,
optionally 2.4 MPa, optionally 2.5 MPa, optionally 2.6 MPa,
optionally 2.7 MPa, optionally 2.8 MPa, optionally 2.9 MPa,
optionally 3 MPa, optionally 3.1 MPa, optionally 3.2 MPa,
optionally 3.3 MPa, optionally 3.4 MPa, optionally 3.5 MPa,
optionally 3.6 MPa, optionally 3.7 MPa, optionally 3.8 MPa,
optionally 3.9 MPa, optionally 4 MPa, optionally 4.1 MPa,
optionally 4.2 MPa, optionally 4.3 MPa, optionally 4.4 MPa,
optionally 4.5 MPa, optionally 4.6 MPa, optionally 4.7 MPa,
optionally 4.8 MPa, optionally 4.9 MPa, optionally 5 MPa,
optionally 5.1 MPa, optionally 5.2 MPa, optionally 5.3 MPa,
optionally 5.4 MPa, optionally 5.5 MPa, optionally 5.6 MPa,
optionally 5.7 MPa, optionally 5.8 MPa, optionally 5.9 MPa. In some
embodiments the hydrogenation pressure is 6 MPa or greater.
[0034] The resulting activated hydrogen storage alloy produced by
the provided processes possesses capacities that nearly double and
often more than double those of compositionally identical materials
produced in traditional manners.
[0035] Various aspects of the present invention are illustrated by
the following non-limiting examples. The examples are for
illustrative purposes and are not a limitation on any practice of
the present invention. It will be understood that variations and
modifications can be made without departing from the spirit and
scope of the invention.
Experimental
[0036] A series of metal hydride alloys of Formula I or II were
prepared and hydrided by various conditions in connection with an
experimental series illustrating the principles of the present
invention. The alloys had the basic design of the following atomic
percentages: Ti 13.6; Zr 2.1; V 44.0; Cr 13.2; Mn 6.9; Fe 2.7; Co
1.4; Ni 15.7; and Al 0.3. The materials were purchased from Chuo
Denki Kogyo and arc melted under conditions of continuous argon
flow using a non-consumable tungsten electrode and a water cooled
copper tray. Prior to formation, the residual oxygen concentration
in the system was reduced by subjecting a piece of sacrificial
titanium to several melt-cool cycles. Study ingots where then
subjected to several re-melt cycles with turning over to ensure
uniformity in chemical composition.
ICP Analyses
[0037] The chemical composition of the prepared alloy samples was
determined using a Varian Liberty 100 inductively coupled plasma
optical emission spectrometer (ICP-OES) in accord with principles
known in the art. The ICP results from ingots prior to activation
in atomic percentage are illustrated in Table 1.
TABLE-US-00001 TABLE 1 Designed compositions and ICP compositional
results in atomic percent. Alloy Ti Zr V Cr Mn Fe Co Ni Al B/A
ratio Design 13.6 2.1 44.0 13.2 6.9 2.7 1.4 15.7 0.3 5.37 ICP 13.8
2.0 43.1 13.1 6.5 2.8 1.4 16.7 0.6 5.33
[0038] The as-cast composition is in excellent agreement with the
composition as designed.
Phase Distribution and Composition
[0039] The alloy phase distribution and composition were examined
using a JEOL-JSM6320F scanning electron microscope with energy
dispersive spectroscopy (EDS) capability. Samples were mounted and
polished on epoxy blocks, rinsed and dried before entering the SEM
chamber. Back scattering electron images are presented in FIG. 1.
Several areas are chosen for study by EDS which are each depicted
with a numeral in FIG. 1. The results of the EDS measurements are
illustrated in Table 2.
TABLE-US-00002 TABLE 2 Numeral Ti Zr V Cr Mn Fe Co Ni Al B/A Phase
1 22.4 9 19.5 2.4 7.1 2.8 1.8 33.8 1 2.18 AB.sub.2 2 36.3 2.4 8.8
1.3 3.9 3.3 3.6 39 1.3 1.58 Zr.sub.xNi.sub.y 3 35.1 8.2 16.1 1.4
4.5 2 1.4 30.8 0.5 1.31 Zr.sub.xNi.sub.y 4 5.7 0.1 58.7 19.2 6.9
2.7 1 5.3 0.5 16.26 BCC 5 1.6 93.1 2.8 1 0.3 0.2 0.1 0.9 0.1 0.06
Zr
Hydriding
[0040] The alloys of Example 1 are subjected to various activation
conditions by varying either the maximum temperature of the alloy
during activation through cooling the system, by altering the
hydrogen pressure, or both. Four activation processes are depicted
in Table 3.
TABLE-US-00003 TABLE 3 Exemplary Activation Conditions As cast Hand
grind (mortar & pestle) Control 1.4 MPa activation @350.degree.
C. Heat Degas @350.degree. C. for 1 hour 1.4 MPa Stabilization
@350.degree. C. Heat Degas @350.degree. C. for 1 hour 1.4 MPa
Stabilization @350.degree. C. Heat Degas @300.degree. C. for 1 hour
1.2 MPa Manual PCT @60.degree. C. Degas @300.degree. C. for 1 hour
1.2 MPa Manual PCT @30.degree. C. Degas @300.degree. C. for 1 hour
Hand grind (mortar & pestle) Example 1 1.4 MPa activation
@300.degree. C. Heat Degas @300.degree. C. for 1 hour 1.4 MPa
Stabilization @300.degree. C. Heat Degas @300.degree. C. for 1 hour
1.4 MPa Stabilization @300.degree. C. Heat Degas @300.degree. C.
for 1 hour Hand grind (mortar & pestle) Example 2 6 MPa
activation + Desorption @30.degree. C. 6 MPa Auto PCT @30.degree.
C. 6 MPa Auto PCT @60.degree. C. Degas @300.degree. C. for 1 hour
Hand grind (mortar & pestle) Example 3 6 MPa activation Degas
@30.degree. C. for 1 hour Hand grind (mortar & pestle)
[0041] The activated alloys of the control using traditional
activation methods and those produced as per the processes of
Examples 1-3 are subjected to analyses for gas phase hydrogen
storage characteristics and electrochemical properties as well as
structural arrangements.
XRD Analyses
[0042] Microstructure of the activated alloys was studied utilizing
a Philips X'Pert Pro x-ray diffractometer. The XRD patterns of the
4 samples (control (a) and Examples 1-3 (b-d, respesctively)) are
shown in FIG. 2. Two sets of diffraction peaks are observed, C14
and BCC, indicating the significance of these structures in the
overall system. The crystallite sizes of each phase are obtained
from full pattern fitting of the XRD data using the Rietveld method
and Jade 9 software. FIG. 3 illustrates the FWHM of the BCC peak
(110) as it is varied between the control and the samples activated
by the new processes. The calculated crystallite sizes of the BCC
phase are presented in Table 4.
TABLE-US-00004 TABLE 4 Crystallite sizes of the BCC (110) phase.
BCC Phase Crystallite HWHM (.degree.) Size (.ANG.) Control 1 0.27
406 Example 1 0.341 298 Example 2 0.474 201 Example 3 0.393 251
[0043] Each of the exemplary activated materials show crystallite
sizes of the BCC phase of less than 300 .ANG..
[0044] Lattice constants a and c from each sample are listed in
Table 5.
TABLE-US-00005 TABLE 5 a c Control 1 4.9004 7.9302 Example 1 4.9005
7.9761 Example 2 4.8939 7.9737 Example 3 4.909 7.9916
Gaseous Phase Characteristics
[0045] The gaseous phase hydrogen storage characteristics of the
control and of Examples 1-3 were measured using a Suzuki-Shokan
multi-channel pressure-concentration-temperature (PCT) system. The
PCT isotherms at 30.degree. C. and 60.degree. C. were then
measured. The resulting absorption and desorption isotherms for the
Control and the alloy active as per Example 1 are presented in FIG.
4.
[0046] The Control material shows significant hysteresis and does
not exceed 1.1% hydrogen weight percentage after activation. The
same material activated by a process that uses the identical
hydrogen gas pressure, but controls the maximum temperature of the
alloy during activation so as not to exceed 300.degree. C. shows
completion of the second plateau and hydrogen weight percentage
above 1.5%.
[0047] The hysteresis of the PCT isotherm is defined as In
(P.sub.a/P.sub.d), where P.sub.a and P.sub.d are the absorption and
desorption equilibrium pressures at the mid-point of desorption
isotherm, respectively. The hysteresis can be used to predict the
pulverization rate of the alloy during cycling. Alloys with larger
hysteresis have higher pulverization rates during
hydriding/dehydriding cycles. From the hysteresis, a large increase
in cycle stability is expected by activating according to the
processes of Examples 1-3. Particularly, by cooling the ingot
during activation so that the maximum temperature does not exceed
300.degree. C., the hysteresis decreases significantly.
Electrochemical Characterization
[0048] The discharge capacity of each alloy (Control or Examples)
was measured in a flooded-cell configuration against a partially
pre-charged Ni(OH).sub.2 positive electrode. For the half-cell
electrochemical studies, each ingot was first ground and then
passed through a 200-mesh sieve. The sieved powder was then
compacted onto an expanded nickel metal substrate by a 10-ton press
to form a test electrode (about 1 cm.sup.2 in area and 0.2 mm
thick) without using any binder. This allowed improved measurement
of the activation behavior. Discharge capacities of the resulting
small-sized electrodes were measured in a flooded cell
configuration using a partially pre-charged Ni(OH).sub.2 pasted
electrode as the positive electrode and a 6M KOH solution as the
electrolyte. The system was charged at a current density of 100
mA/g for 5 h and then discharged at a current density of 50 mA/g
until a cut-off voltage of 0.9 V was reached. The system was then
discharged at a current density of 12 mA/g until a cut-off voltage
of 0.9 V was reached and finally discharged at a current density of
4 mA/g until a cut-off voltage of 0.9 V was reached.
[0049] The obtained half-cell capacities are illustrated in Table
6.
TABLE-US-00006 TABLE 6 Summary of electrochemical properties of
alloys active by control or exemplary processes. 50 mAh/g 4 mAh/g
Control 167 172 Example 1 308 346 Example 2 354 375 Example 3 294
322
[0050] Overall, compared to the control sample, those activated
using cooling to 300.degree. C. or less or activated by increased
hydrogen pressure showed: greatly improved electrochemical
capacities of nearly 300 mAh/g or greater; increased capacities gas
phase capacity; and flatter PCT isotherms with decreased
hysteresis.
[0051] Patents, publications, and applications mentioned in the
specification are indicative of the levels of those skilled in the
art to which the invention pertains. These patents, publications,
and applications are incorporated herein by reference to the same
extent as if each individual patent, publication, or application
was specifically and individually incorporated herein by
reference.
[0052] In view of the foregoing, it is to be understood that other
modifications and variations of the present invention may be
implemented. The foregoing drawings, discussion, and description
are illustrative of some specific embodiments of the invention but
are not meant to be limitations upon the practice thereof. It is
the following claims, including all equivalents, which define the
scope of the invention.
* * * * *
References