Electrochemical performance of gas-atomized MmNi5-based alloy powders

A series of MmNi(5)-based (Mm-Ni-Co-Mn-Al) alloy powders were prepared by gas atomization. On hydrogenation, a large discontinuous volume change produced extensive fracture in all alloy powders except those smaller than 10 mum. Annealing does not affect the P-C-T characteristics, but improves the cyclic stability of the electrochemical discharge. The discharge capacity varies with the composition and particle size. There is a trade-off in the contents of Co and Mn for electrochemical performance. A higher content of Co and a lower content of Mn gives a small electrochemical capacity, but a longer cycle life. A medium content of Co and Mn results in a higher discharge capacity and decay rate. The particle size seems to be a very important factor influencing the electrochemical activation kinetics. The fracture of larger particles induced by charging creates fresh surfaces for easier hydrogenation. (C) 2003 Elsevier B.V. All rights reserved.