Properties of composites of metal hydride alloys synthesized by mechanical milling

Hydride-forming alloys are used as negative electrode components of nickel metal hydride (MH) batteries. Generally, commercially used compounds are made of two types of alloys, rare earth based on LaNi 5 , known as AB 5 type, and alloys based on ZrCr 2 , ZrV 2 , ZrMn 2 , and TiMn 2 , known as AB 2 type (Laves phases). A and B are generally composed of more than one element. In both systems, the A components are metals that form stable hydrides, while the B components are transition metals and form less stable hydrides. In the present work, electrodes were prepared using composite material obtained by mechanical milling of different proportions of ZrTiV 0.8 Ni 2 Cr 0.52 Mn 0.56 Co 0.08 Al 0.04 (AB 2 ) and LaNi 3.6 Co 0.7 Mn 0.4 Al 0.3 (AB 5 ) alloys. The particles of the AB 5 alloy were dispersed on the surface of the AB 2 particles, as shown by scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). The discharge capacity of the electrodes improved with the addition of 80 and 50 weight-% AB 2 . The maximum discharge capacities obtained, after 30 cycles, for electrodes with 50 and 80 % AB 2 were above 200 mA h g −1 , while for the original AB 2 alloy it was less than 170 mA h g −1 . A decrease in the composite concentration of the AB 2 alloy improves the exchange current density, as can be seen from electrochemical impedance spectroscopy (EIS) measurements. High-rate dischargeability (HRD) and EIS results showed enhanced hydrogen diffusion for the samples with an AB 2 concentration of 50 and 80 %.