Nickel-metal hydride battery using nanocrystalline TiFe-type hydrogen storage alloys

Article abstract of DOI:10.1016/j.jallcom.2004.09.084

Mechanical alloying (MA) process was used to synthesize nanocrystalline TiFe-type alloys. XRD analysis showed that, firstly, after 20 h of milling, the starting mixture of the elements had transformed into an amorphous phase and, secondly, the annealing i

Full text of DOI:10.1016/j.jallcom.2004.09.084

Journal of Alloys and Compounds 404–406 (2005) 691–693
Nickel–metal hydride battery using nanocrystalline
TiFe-type hydrogen storage alloys
a,∗
b
b
E. Jankowska , M. Makowiecka , M. Jurczyk
a
Central Laboratory of Batteries and Cells, Forteczna 12 St., 61-362 Poznan, Poland
Institute of Materials Science and Engineering, Poznan University of Technology, M. Sklodowska Curie 5 Sq.,
0-965 Poznan, Poland
b
6
Received 31 May 2004; received in revised form 3 September 2004; accepted 15 September 2004
Available online 16 November 2005
Abstract
Mechanical alloying (MA) process was used to synthesize nanocrystalline TiFe-type alloys. XRD analysis showed that, firstly, after 20 h
of milling, the starting mixture of the elements had transformed into an amorphous phase and, secondly, the annealing in high purity argon at
◦
7
00 C for 0.5 h led to formation of the CsCl-type structures with crystallite sizes of about 30 nm. It was found that the respective replacement
of Fe in TiFe by Ni and/or by Al and Cr improved both the discharge capacity and the cycle life of these electrodes. In the nanocrystalline
−
1
−1
TiFe0.125Cr0.125Ni0.75 powder discharge capacity up to 154 mA h g was measured (at 40 mA g discharge current). Some of the produced
nanomaterials were used as negative electrodes in sealed Ni/MH button cells. The results show that the sealed battery using the nanocrystalline
TiFe0.25Ni0.75 or TiFe0.3Ni0.5Co0.2Zr0.05 alloys have about 1.5 times the capacity of the TiFe one.
©
2005 Published by Elsevier B.V.
Keywords: Fuel cells; Metal hydrides; Nanostructured materials; Mechanical alloying
polycrystalline form was 0.07 mAh g 1 at discharge current
of 4 mA h [8]. The property of this alloy can be stimulated by
partial replacement of iron by some amount of transition met-
alsintheTiFesystemorbymodificationofthemicrostructure
which may improve the properties of the alloy for practical
use, e.g. as active material in MH electrode [4,9,10]. Earlier,
the effect of high-energy ball-milling (HEBM) on the elec-
trochemical properties of TiFe electrode material has been
investigated [10]. The discharge capacity of HEBM TiFe ma-
−
1
. Introduction
The nickel–metal hydride (Ni/MH) cell has a hydrogen
storage material as its negative electrode, which is able to
absorb and desorb reversibly a large amount of hydrogen at
room temperature [1–4]. These batteries attracted increasing
attention due to its various advantages. They widely are used
from communication to hybrid electric vehicles.
The polycrystalline TiFe(Ni) system has been widely stud-
ied in the past [4–7]. TiFe alloy, which crystallizes in the
cubic CsCl-type structure, can absorb up to 2 H/f.u. at room
temperature. After activation the TiFe reacts directly and re-
versibly with hydrogen to form two ternary hydrides TiFeH
−
1
terial increased to 64 mAh g
.
During last years, mechanical alloying (MA) has been
proved to be a promising method for preparation of the wide
range of materials for energy storage or other energy-related
applications [4]. The use of mechanical alloying technique
is very effective in lowering the cost of hydrogen storage
materials.
In present work, we have shown that the properties of
nanocrystalline TiFe-type alloys can be stimulated by partial
replacement of iron by some amount of transition metals (Ni,
Al, Cr, Co, Mo or Zr). These alloys produced by mechanical
(orthorhombic) and TiFeH2 (monoclinic). The application of
TiFe material in cells has been limited due to poor absorp-
tion/desorption kinetics in addition to a complicated activa-
tion procedure [6]. The discharge capacity of TiFe alloy in
∗
Corresponding author. Fax: +48 61 879 30 12.
E-mail address: jankowska ewa@o2.pl (E. Jankowska).
0
925-8388/$ – see front matter © 2005 Published by Elsevier B.V.
doi:10.1016/j.jallcom.2004.09.084

6
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E. Jankowska et al. / Journal of Alloys and Compounds 404–406 (2005) 691–693
alloying followed by annealing were used as negative elec-
trode for testing the charge/discharge cycles in half-cells and
in sealed Ni/MH cells.
2
. Experimental details
The nanocrystalline TiFe-type powders were prepared by
MA and annealing the stoichiometric amounts of the con-
stituent elements (the purity more than 99.8 wt.%). These ma-
terials were processed under a high purity argon atmosphere
using SPEX 8000 Mixer Mill (USA). The elemental powders
were mixed in glove box (Labmaster 130) and poured into
the vial. The mill was run up to 25 h for every powder prepa-
◦
ration. The as-milled powders were heat-treated at 700 C for
0
Fig. 1. XRD spectra of nanocrystalline Ti and Fe powders mechanically
alloyed in argon atmosphere for 25 h (a) and heat-treated at 700 C for 0.5 h
◦
.5 h under high purity argon to form CsCl-type phase. The
MA process has been studied by X-ray powder diffraction
analysis with Co K␣1 radiation at the various stages during
milling. Crystallite sizes were determined by atomic force
microscopy (AFM).
The mechanically alloyed and annealed (nanocrystalline)
materials with 10 wt.% addition of tetracarbonylnickel pow-
der, were subjected to electrochemical measurements as
working electrodes. A detailed description of the electro-
chemical measurements was given in Refs. [8–10].
The cyclic behavior of the nanocrystalline alloy anodes
was examined in a sealed HB 116/054 cell (according to the
international standard IEC no. 61808, related to the hydride
button rechargeable single cell) [11]. The mass of the ac-
tive material was 0.33 g. To prepare MH negative electrodes,
alloy powders were mixed with addition of 5 wt.% tetracar-
bonylnickel. Then this mixture was pressed into the tablets
which were placed in a small basket made of nickel nets
(b).
(
Table 1). When nickel is substituted for iron in TiFe1−xNix
the lattice constant a increases.
The average crystallite size of the nanocrystalline TiFe
powders, according to AFM studies, was of the order of
30 nm.
The discharge capacity of electrodes prepared by appli-
cation of mechanically alloyed TiFe alloy powder is very
low (Fig. 2) though the MA TiFe alloys showed a higher dis-
−
1
charge capacity (0.7 mA h g ) than the arc melted ones. The
reduction of the powder size and the creation of new surfaces
is effective for the improvement of the hydrogen absorption
rate. Materials obtained by the substitution of Ni for Fe in
TiFe1−xNix lead to great improvement in activation behav-
ior of the electrodes. It was found that the increasing nickel
content in TiFe1−xNix alloys leads initially to an increase in
discharge capacity, giving a maximum at x = 0.75 (Fig. 2).
(as the current collector). The sealed Ni/MH cell was con-
In the annealed nanocrystalline TiFe0 Ni
powder, dis-
0.75
.25
structed by pressing together the negative and positive elec-
−
1
−
3
charge capacity of up to 155 mA h g was measured. The
electrodes mechanically alloyed and annealed from the ele-
mental powders displayed the maximum capacities at around
the 3rd but, especially for x = 0.75 in TiFe1−xNix alloy, de-
graded slightly with cycling. This may be due to the easy
formation of the oxide layer (TiO2) during the cycling. On
the other hand, the discharge capacity of nanocrystalline
trode, polyamide separator and KOH (ρ = 1.20 g cm ) as
electrolyte solution. The cell with electrode fabricated from
nanocrystalline materials was charged at current density of
−
1
i = 3 mA g for 15 h and after 1 h pause discharged at cur-
−
1
rent density of i = 7 mA g down to 1.0 V. All electrochem-
◦
ical measurements were performed at 20 ± 1 C.
Table 1
3
. Results and discussion
Structural parameters and discharge capacities of nanocrystalline TiFe-type
materials on 3rd cycle in half-cell (current density of charge/discharge was
−
1
The effect of MA processing was studied by X-ray diffrac-
40 mA g
)
tion. For example, in the case of Ti–Fe powder mixture the
originally sharp diffraction lines of Ti and Fe gradually be-
come broader and their intensity decreases with milling time
Composition
a
Discharge capacity
On 3rd cycle
On 10th cycle
TiFe
TiFe0.25Ni0.75
2.973
3.010
3.013
3.011
3.010
3.013
3.012
3.018
0.7
155
140
154
113
122
128
67
–
133
120
134
105
100
126
67
(not presented in Fig. 1). The powder mixture milled for more
than 20 h has transformed completely to the amorphous phase
TiFe0.125Al0.125Ni0.75
TiFe0.125Cr0.125Ni0.75
TiFe0.125Co0.125Ni0.75
TiFe0.125Mo0.125Ni0.75
TiFe0.3Ni0.5Co0.2Zr0.05
TiNi
(
(
“X-ray-amorphous”), without formation of other phases
Fig. 1). Formation of the nanocrystalline alloys was achieved
by annealing of the amorphous material in high purity argon
◦
atmosphere at 700 C for 0.5 h. For all studied compositions,
the diffraction peaks were assigned to CsCl-type structures

E. Jankowska et al. / Journal of Alloys and Compounds 404–406 (2005) 691–693
693
discharge capacity in comparison to basic alloy. In nanocrys-
talline TiFe0.125Cr0.125Ni0.75 powders discharge capacities
−
1
up to 160 mAh g was measured (Fig. 3) (Table 2).
4. Conclusion
In conclusion, nanocrystalline TiFe-based alloys synthe-
sized by MA and annealing were used as negative electrode
materials for Ni/MH cell. The discharge capacity of electrode
prepared by application of MA and annealed TiFe powder
displayed low capacity. It was found that the replacement
of Fe in TiFe by Ni and/or by Al and Cr improved not
only the discharge capacity but also the cycle life of these
electrodes. Some of the studied alloys were used as negative
electrodes for sealed Ni/MH cells. The results show that
the sealed cells using the nanocrystalline TiFe0.25Ni0.75
and TiFe0.3Ni0.5Co0.2Zr0.05 alloys have about 1.5 times the
capacity of the TiFe one.
Fig. 2. Discharge capacities as a function of cycle number of electrodes
prepared with nanocrystalline: (a) TiFe; (b) TiFe0.25Ni0.75; (c) TiNi powders
−
1
(
6 M KOH solution; the charge/discharge conditions were 40 mA g and
the cut-off potential was −0.700 V).
Acknowledgements
The glove box Labmaster 130 (M. Braun-Germany) was
purchased by the Foundation for Polish Science under the
program TECHNO’2000. Financial support forthiswork was
provided by the Polish National Committee for Scientific Re-
search (KBN) under contract No. 4T10A 00522. One of us
Fig. 3. Discharge capacities as a function of cycle number of elec-
trodes prepared with nanocrystalline: (a) TiFe0.3Ni0.5Co0.2Zr0.05, (b)
TiFe0.125Al0.125Ni0.75, (c) TiFe0.125Cr0.125Ni0.75, (d) TiFe0.125Co0.125Ni0.75
and (e) TiFe0.125Mo0.125Ni0.75 powders (6 M KOH solution; the
(E.J.) has been supported by the Fellowship from the Foun-
dation for Polish Science (2004).
−
1
charge/discharge conditions were 40 mA g and the cut-off potential was
0.700 V).
−
Table 2
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