Electrochemical properties of Zr(VxNi1-x)(3) as electrode material in nickel metal hydride batteries

Zr-V-Ni based alloys represent one group of alloys with promising propertie s for the use as hydrogen absorbing electrodes in an alkaline electrolyte. In particular, this group has been studied because these alloys are effecti ve in overcoming the energy density limitations of present AB(5) type alloy s. We have investigated the alloys Zr(VxNi1-x)(3) in the range 0.29 less than or equal to x less than or equal to 0.5 by means of scanning electron micro scopy (SEM) with electron probe X-Ray microanalysis (EPMA), X-ray diffracti on (XRD) and electrochemical measurements. The alloys are composed of different crystallographic phases. The main phas e (a C15 laves phase, space group Fd3m) consists of all three elements and was found to be responsible for the high reversible capacity of a maximum o f 375 mAh/g. The second phase is vanadium-nickel based (b.c.c. structure, s pace group: Im3m). The discharge kinetics of this alloys was investigated in electrochemical e xperiments. We observed an increase of the high rate dischargeability with increasing nickel content. This is mainly due to the catalytic effect of ni ckel for the hydrogen absorption-desorption process. The exchange current d ensity increases with increasing nickel content. Furthermore: we observed a faster activation for the alloys with higher nickel content. (C) 1999 Inte rnational Association for Hydrogen Energy. Published by Elsevier Science Lt d. All rights reserved.