ELECTROCHEMICAL PROPERTIES OF ZR-V-NI SYSTEM HYDROGEN-ABSORBING ALLOYS OF FACE-CENTERED CUBIC STRUCTURE

The alloy composition dependence of the electrochemical properties was investigated in the Zr-V-Ni hydrogen-absorbing alloys for the development of nickel-hydride secondary batteries. Thus, for the Zr(V1-xNix)2, (0.1≦x≦1.0) and Zr(V0.33Ni0.67)2+α, (0≦α≦1) system alloys, charged hydrogen contents by electrolysis, discharge characteristics and changes in the partial molar enthalpy and entropy with hydrogenation were investigated in an alkaline electrolyte. It was found that the Zr(V0.33Ni0.67)2+α, (0≦α≦1) system alloys which consist of a single phase of the f.c.c. structure exhibit large discharged hydrogen capacities, especially at α=0.4. By increasing α, their polarization, characteristics were improved and the partial molar enthalpy of hydrogen in the metals considerably increased. Furthermore, from the values of the charged hydrogen contents and the results of the X-ray investigations, it was found that hydrogen mainly occupies the Zr2V1Ni1, tetrahedral lattice interstitials for the Zr(V0.33Ni0.67)2+α alloys. The increase in the partial molar enthalpy of hydrogen in the metals and the improvement in the polarization characteristics by an excess of V and Ni could be understood from the lattice contract effect of the host metals. © 1990, The Japan Institute of Metals. All rights reserved.