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

The phase structures and electrochemical properties of the V3TiNi0.56Hf0.24 Cox 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 solut ion with b.c.c. structure and the secondary phase is an under-stoichiometri c C14-type Laves phase of (Ti, Hf)(V, Co, Ni)(m) (m<2) with hexagonal struc ture. With increasing Co content, the lattice parameters of both the main p hase 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 el ectrodes in KOH solution. In addition, because of the poor reaction kinetic s 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. A ll rights reserved.