A. Zuttel et al., RELATIONSHIP BETWEEN COMPOSITION, VOLUME EXPANSION AND CYCLIC STABILITY OF AB(5)-TYPE METALHYDRIDE ELECTRODES, Journal of alloys and compounds, 253, 1997, pp. 626-628
Metal hydride alloys as electrode material for battery application con
tain up to 15 at.% cobalt. Alloys without cobalt show a much shorter c
ycle life compared to cobalt containing alloys. The mechanism of how c
obalt influences the cycle life is still not well understood. The aim
of this work is to investigate the influence of cobalt on the properti
es of the electrode. A series of alloys with different cobalt content
and several other substituents for nickel (Fe, Cu,...) were prepared i
n two different ways. A set of samples was conventionally melted. A se
cond set of samples was prepared by gas atomization. The volume expans
ion upon hydriding was analyzed by means of X-ray diffraction. Electro
chemical measurements, e.g., discharge capacity as a function of cycle
number, were performed. The volume expansion upon hydriding decreases
with increasing cobalt content of the alloy. Cobalt substitution for
nickel improves the cycle life of an electrode, especially at elevated
temperatures (40 degrees C). However, alloys where cobalt is partiall
y substituted by iron show an even better cyclic stability and rate ca
pability.