Electrochemical and crystallographic characterization of Co-free hydrogen storage alloys for use in nickel-metal hydride batteries

Electrochemical and crystallographic characterization of Co-free hydrogen s torage alloys containing Si and/or Fe was carried out. In the charge-discha rge cycle test, the maximum discharge capacity of a Co-free MmNi(4.3)Mn(0.4 )Al(0.3) (Mm = misch metal) alloy electrode was decreased by the partial su bstitution of Si and/or Fe for Ni, but the cycle performance was improved. The MmNi(3.6)Mn(0.4)Al(0.3)Si(0.1)Fe(0.6) electrode showed the most excelle nt cycle durability in this study. It was found by SEM, EPMA and XRD that F e and Si contained in these alloys more or less suppressed the dissolution of Al and the lattice expansion with hydrogen absorption, leading to the lo ng cycle Hfe. This effect was strengthened by the simultaneous partial subs titution of Si and Fe for Ni in the Co-free alloy. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.