Synthesis and characterisation of the nanostructured magnesium-lanthanum-nickel alloys for Ni-metal hydride battery applications
Affordable price, high abundance of magnesium and high densities of hydrogen
in the Mg-based hydrides attract interest to these hydrides tailored for hydrogen
and energy storage applications. Ternary La-Mg-Ni hydrogen storage alloys with
composition La3-xMgxNi9 (x = 0.8-1.2) form a new class of the materials for the
negative electrodes in Ni-Metal Hydride (MH) batteries. The electrochemical discharge
capacity of such alloys reaches 400 mAh/g which is 25 % greater than that
of the commercial AB5-type based electrodes, 315 mAh/g. The La3-xMgxNi9
alloys crystallize with trigonal PuNi3 type of crystal structure. Magnesium replaces
lanthanum to form the hybrid LaNi5 + Laves phase structures and favorably
changes the thermodynamics of the metal-hydrogen interactions allowing
improved performance of the advanced metal hydride battery electrodes.
Differences in melting temperatures of lanthanum, nickel and easily evaporating
magnesium and a complexity of the phase equilibria in the La-Mg-Ni system
cause difficulties in synthesis of the battery electrode alloys with controlled Mg
content and a desired phase-structural composition.
In present work a La2MgNi9 alloy was in focus. Its successful synthesis has
been achieved from the alloy melts containing 0-30 % of overstoichiometric Mg
as compared to La2MgNi9 by use of Rapid Solidification performed at various
quenching rates, with a copper wheel rotation speed of 3.1, 10.5 and 20.9 m/s.
They were analyzed by synchrotron X-ray diffraction (SR XRD) including in situ
studies in hydrogen gas performed at Swiss-Norwegian Beam Lines at ESRF,
Grenoble, and by Scanning Electron Microscopy (SEM) with electron probe
microanalysis (EPMA). Pressure-Composition-Temperature isotherms, hydrogen
absorption-desorption cycling and measurements of the electrochemical chargedischarge
performances were employed to characterize hydrogenation behaviors
of the studied alloys. These studies showed that the melt spinning of the alloy
containing 30 % weight excess of Mg quenched using wheel spin speed of 400 RPM
allowed obtaining the most homogeneous sample with the optimal microstructure
and phase-structural composition corresponding to the formation of La2MgNi9
with the highest yield.
Variations in magnesium content and selection of optimal conditions for the Rapid
Solidification process provide complementary possibilities in improving properties
of the studied La-Mg-Ni alloys as hydrogen storage and battery electrode
materials and provide a possibility to upscale production of the battery alloys.
This work was performed at Institute for Energy Technology and at Department
of Materials Science and Engineering, NTNU.
Place, publisher, year, edition, pages
Institutt for materialteknologi , 2012. , 74 p.
ntnudaim:7442, MTMT Materialteknologi, Materialer og energiteknologi
IdentifiersURN: urn:nbn:no:ntnu:diva-18466Local ID: ntnudaim:7442OAI: oai:DiVA.org:ntnu-18466DiVA: diva2:565958
Yartys, Volodymyr, Professor IISolberg, Jan Ketil