An electrochemical investigation of melt-spun nanocrystalline and amorphous Mg2Ni-type electrode alloys

Nanocrystalline and amorphous Mg2Ni-type M20-xLaxNi10 (x= 0, 2,4,6) electrode alloys were synthesized by the melt-spinning technique. The microstructures of the as-quenched ribbons were characterized by XRD, HRTEM and electron diffraction (ED). The electrode properties of these alloys were measured. The experimental results show that no amorphous phase forms in the as-quenched La-free alloy, but the asquenched alloys containing La hold a major amorphous phase, confirming that the substitution of La for Mg significantly increases the glass forming ability of the Mg2Ni-type alloys. The discharge capacities of the as-cast alloys increase with rising La content, but those of the as-quenched alloys first increase and then decrease with the variety of La content. The largest discharge capacity reaches around 406.5 mA h/g at a discharge current density of 20 mA/g for the Mg18La2Ni10 sample quenched at 30 m/s. The substitution of La for Mg significantly intensifies the cycle stability of the alloys. When La content grows from 0 to 6, the capacity retaining rate of the as-quenched (15 m/s) alloy after 15 cycles rises from 37.18 to 94.93%, and from 35.29 to 95.99% for quenching rate of 30 m/s, respectively. Rapid quenching engenders impactful effects on the electrochemical performances of the experimental alloys, involving the increased discharge capacity except x = 6 and the strengthened cycle stability, which means that the improvement of electrochemical performances is not only a function of the sample composition but also strongly influenced by the proportion of the nanocrystalline and amorphous phase in the alloys. (c) 2008 Elsevier B.V. All rights reserved.