Influence of polymorphism on the electrochemical properties of (Ti0.64Zr0.36)Ni alloys

Key electrochemical properties of austenitic and martensitic (Ti0.64Zr0.36)Ni alloys as regards their use as negative electrodes for Ni-MH batteries have been studied. Austenitic alloys exhibit a reversible capacity of 85 mAh / g, at a discharging rate of C / 10, without notable capacity decay upon electrochemical cycling. In contrast, martensitic alloys possess, at the same regime, a much higher reversible capacity, 330 mAh/g, though a shorter cycle-life. These dissimilar results are due to the remarkable thermodynamic differences for hydrogen absorption between both structures. Besides, it has been observed that both phases neither decompose nor suffer any phase transformation upon repeated hydrogen absorption/ desorption cycling. Capacity decay in martensite seems to be associated to surface passivation effects which are favoured by mechanical decrepitation. (C) 2003 Elsevier B.V. All rights reserved.