Rare earth–Mg–Ni-based hydrogen storage alloys as negative electrode materials for Ni/MH batteries

This review is devoted to new rare earth–Mg–Ni-based (R–Mg–Ni-based) hydrogen storage alloys that have been developed over the last decade as the most promising next generation negative electrode materials for high energy and high power Ni/MH batteries. Preparation techniques, structural characteristics, gas–solid reactions and electrochemical performances of this system alloy are systematically summarized and discussed. The improvement in electrochemical properties and their degradation mechanisms are covered in detail. Optimized alloy compositions with high discharge capacities, good electrochemical kinetics and reasonable cycle lives are described as well. For their practical applications in Ni/MH batteries, however, it is essential to develop an industrial-scale homogeneous preparation technique, and a low-cost R–Mg–Ni-based electrode alloy (low-Co or Co-free) with high discharge capacity, long cycle life and good kinetics.

Research highlights▶ State-of-the-art of new R-Mg-Ni-based hydrogen storage electrode alloys is reviewed. ▶ Electrode performances of the R-Mg-Ni-based alloys depend strongly on the stoichiometric ratio, alloy components and microstructure. ▶ Optimized alloy compositions contain mainly metallic elements of La, Mg, Ni, Co, Mn and Al. ▶ Pulverization of particles and oxidation/corrosion of active components are responsible for the fast capacity degradation. ▶ Low-Co or Co-free R-Mg-Ni-based electrode alloys should be developed.