Nanocrystalline titanium-type metal hydride electrodes prepared by mechanical alloying

Abstract

Mechanical alloying (MA) was employed to produce nanocrystalline TiFe1−xNix alloys (x=0, 0.25, 0.5, 0.75 and 1.0). XRD analysis showed that, after 25 h of milling, the starting mixture of the elements had decomposed into an amorphous phase. Following annealing in high purity argon at 750°C for 0.5 h, XRD confirmed the formation of the CsCl-type structures with crystallite sizes of about 50 nm. These materials were used as negative electrodes for a Ni–MHx battery. With increasing nickel content in TiFe1−xNix, the material shows an increase in discharge capacity which passes through a maximum for x=0.75. In the nanocrystalline TiFe0.25Ni0.75 powder, discharge capacities of up to 155 mA h g−1 (at 40 mA g−1 discharge current) were measured. The titanium-based hydrogen storage alloys are attractive for secondary batteries, because of inexpensive raw materials.