H. Nakano et S. Wakao, SUBSTITUTION EFFECT OF ELEMENTS IN ZR-BASED ALLOYS WITH LAVES PHASE FOR NICKEL-HYDRIDE BATTERY, Journal of alloys and compounds, 231(1-2), 1995, pp. 587-593
By examining the electrochemical and thermodynamic properties of Zr(1-
x)A'(x)(VyNizMnuB'(v))(2+alpha) (0 less than or equal to x less than o
r equal to 0.1; 0.10 less than or equal to y less than or equal to 0.1
5; 0.41 less than or equal to z less than or equal to 0.62; 0.28 less
than or equal to u less than or equal to 0.39; 0 less than or equal to
v less than or equal to 0.05; 0 less than or equal to alpha less than
or equal to 0.02; y + z + u + v = 1; A' = Ti, Nb; B' = Co, Cr, Cu, Fe
) alloy systems with C15-type Laves phase structure, the results descr
ibed below were obtained. The alloy electrodes were completely activat
ed even by one or two charge-discharge cycles at a current density of
17 mA g(-1). Some of the alloys had discharge capacities larger than 4
00 mA h g(-1) at 17 mA g(-1). They also had capacities larger than 380
mA h g(-1) even at 220 mA g(-1). Moreover, the high rate capability f
or discharge increased as the absolute value of the partial molar enth
alpy Delta H-o for hydride formation decreased. The Delta H-o values o
f such alloys with excellent electrochemical properties were found to
range from -36 to -42 kJ mol H-2(-1). On the other hand, the substitut
ion effect of the elements in the alloys was qualitatively and quantit
atively evaluated as a function of the atomic radii and electronegativ
ities of the constituent elements. Delta H-o, which shows the stabilit
y of the absorbed hydrogen, had a good correlation individually with t
he average electronegativity chi(av) and the average atomic radius r(a
v). The correlation was further improved when these two factors were c
onsidered together. The cell volume of C15 type had a correlation with
Delta H-o and a good correlation with both the average atomic radius
and the difference Delta(chi B-A) in electronegativity between the A a
nd B atoms. From the above description it can be concluded that the ra
nges of r(av) and chi(av) of the alloys with excellent capacity and hi
gh rate efficiency are 1.516 less than or equal to r(av) less than or
equal to 1.525 and 1.621 less than or equal to chi(av) less than or eq
ual to 1.640 respectively.