Influence of cobalt content in MmNi4.3-xMn0.3Al0.4Cox alloy (x=0.36 and 0.69) on its electrochemical behaviour studied by in situ neutron diffraction

Ni-MH batteries have been widely studied and improved in recent years. Most of the negative electrodes of such batteries are made from LaNi5-type alloys and improved materials have been obtained from pseudo-binary phases such as MmNi(3.55)Mn(0.4)Al(0.3)Co(0.75). The advantage of cobalt addition has been demonstrated in terms of life-cycle improvement and corrosion resistance. However, cobalt remains the most costly element of the alloy. The behaviour of two electrodes with different cobalt amounts (5 and 10 wt.%) has been investigated by in situ neutron powder diffraction. The appearance of an intermediate gamma phase during the charge process in the 10 wt.% Co alloy is observed and its role in the electrochemical process described. Crystallographic, electrochemical and kinetic behaviour of these electrodes are discussed in relation to cobalt concentration. (C) 1999 Elsevier Science S.A. All rights reserved.