Electrochemical performance of gas-atomized MmNi5-based alloy powders

A series of MmNi5-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 μm. 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.