Electrochemical study of LaNi3.55Mn0.4Al0.3Fe0.75 as negative electrode in alkaline secondary batteries

Cobalt-free AB5-type hydrogen storage alloys have been examined for the purpose of lowering metal hydride raw material costs. For this purpose, the electrochemical behaviour of cobalt-free LaNi3.55Mn0.4Al0.3Fe0.75 alloy was investigated using chronopotentiometry and electrochemical impedance spectroscopy. It was shown that the discharge capacity decreases by 50% after fifty cycles. To investigate the capacity decrease, the impedance measurements were conducted during charging at different stages of life cycle. The experimental impedance spectroscopy reveals that the metal hydride electrode exhibits a porous behaviour. The results were then analyzed on the basis of equivalent circuit model involving the porous electrode behaviour according to de Levie's model, i.e. equivalent cylindrical pores connected in parallel. The pore texture of electrode material was then estimated namely by the pore number, mean values of cylinder radius and effective length. The loss of discharge capacity is due to that of the reactivity of the electrode material and not the collapsing of pore texture.