Intermetallic compounds as negative electrodes of Ni/MH batteries

This review is devoted to the main families of thermodynamically stable intermetallic compounds (AB(5)-, AB(2)- and AB-type alloys) that have been researched in the last thirty years as materials for negative electrodes in nickel-metal hydride batteries. The crystal structure of these compounds and their hydrides is widely described. Their solid-gas hydrogenation properties and, particularly, the related desorption isotherm curves are examined as a useful criterion for the selection of suitable battery materials. The electrochemical performances obtained with these alloys are reported and the given solutions to common problems such as corrosion, passivation, decrepitation and short cycle life are discussed. Only AB(5)-based compounds have achieved, up to now, enough development for being widely present on the market. and exhibit improved battery performances in comparison with the polluting Ni/Cd batteries. The high capacity of AB(2)-based compounds and the remarkable electrochemical activity of some AB-based alloys make, however, further research on all the reviewed families still valuable.