Phase structures and electrochemical properties of V3TiNi0.56Hf0.24Cox alloys

The phase structures and electrochemical properties of the V3TiNi0.56Hf0.24Cox alloys have been studied. It is found that the addition of Co into the V3TiNi0.56Hf0.24 alloy decreases the amount of the main phase and increases the amount of the secondary phase. The main phase is a V-based solid solution with b.c.c. structure and the secondary phase is an under-stoichiometric C14-type Laves phase of (Ti, Hf)(V, Co, Ni)(m) (m<2) with hexagonal structure. With increasing Co content, the lattice parameters of both the main phase and the secondary phase decrease. This leads to a decreasing stability of the alloy hydride and deterioration in discharge capacity of the alloy electrode. However, increasing Co content improves the durability of the electrodes in KOH solution. In addition, because of the poor reaction kinetics of the Laves phase due to inadequate Ni content, the V3TiNi0.56Hf0.24Cox alloys show poorer high rate capabilities. (C) 2000 Elsevier Science S.A. All rights reserved.