Intermetallic compounds as negative electrodes of Ni/MH batteries

This review is devoted to the main families of thermodynamically stable int ermetallic compounds (AB(5)-, AB(2)- and AB-type alloys) that have been res earched in the last thirty years as materials for negative electrodes in ni ckel-metal hydride batteries. The crystal structure of these compounds and their hydrides is widely described. Their solid-gas hydrogenation propertie s and, particularly, the related desorption isotherm curves are examined as a useful criterion for the selection of suitable battery materials. The el ectrochemical performances obtained with these alloys are reported and the given solutions to common problems such as corrosion, passivation, decrepit ation and short cycle life are discussed. Only AB(5)-based compounds have a chieved, up to now, enough development for being widely present on the mark et. and exhibit improved battery performances in comparison with the pollut ing Ni/Cd batteries. The high capacity of AB(2)-based compounds and the rem arkable electrochemical activity of some AB-based alloys make, however, fur ther research on all the reviewed families still valuable.