Electrochemical properties of Zr (V xNi1− x) 3 as electrode material in nickel-metal hydridebatteries

Abstract

Zr-V-Ni based alloys represent one group of alloys with promisingproperties for the use as hydrogen absorbing electrodes in an alkaline electrolyte. In particular,this group has been studied because these alloys are effective in overcoming the energy densitylimitations of present AB 5 type alloys. We have investigated the alloys Zr (V xNi 1−x) 3 in therange 0.29⩽x⩽0.5 by means of scanning electron microscopy (SEM) with electron probe X-Raymicroanalysis (EPMA), X-ray diffraction (XRD) and electrochemical measurements. The alloys are composed of different crystallographic phases. The main phase (a C15laves phase, space group Fd3m) consists of all three elements and was found to be responsible forthe high reversible capacity of a maximum of 375 mAh/g. The second phase is vanadium-nickelbased (b.c.c. structure, space group: Im3m). The discharge kinetics of this alloys was investigated in electrochemical experiments. Weobserved an increase of the high rate dischargeability with increasing nickel content. This is mainlydue to the catalytic effect of nickel for the hydrogen absorption-desorption process. The exchangecurrent density increases with increasing nickel content. Furthermore, we observed a fasteractivation for the alloys with higher nickel content.