Rare earth-Mg-Ni-based alloys with superlattice structure for electrochemical hydrogen storage

Highlights: • Hydrogen storage thermodynamics and kinetics of R-Mg-Ni-based alloys are reviewed. • Approaches for tuning the electrochemical performance of alloys are summarized. • Challenges in developing superlattice R-Mg-Ni-based alloys are pointed out. -- Abstract: The rapid development of Ni-MH batteries urgently needs advanced hydrogen storage alloys as negative electrodes. Rare earth-Mg-Ni-based (R-Mg-Ni-based) hydrogen storage alloys with superlattice structures possess high capacity, good electrochemical properties, moderate hydrogen equilibrium pressure and environment-friendliness, making them the attractive alloys for high-performance Ni-MH batteries. This review focuses on the progress in the superlattice R-Mg-Ni-based hydrogen storage alloys. The structural characteristics, hydrogen storage thermodynamics and kinetics, and approaches for improving electrochemical properties are highlighted. Preparation techniques and composition optimization as the key factors for tuning the electrochemical performance of R-Mg-Ni-based alloys are systematically summarized in this review. New ideas and approaches are still required for developing R-Mg-Ni-based alloys with higher energy density, longer cycle life, better kinetics and lower cost. The challenges and future directions in developing high-performance Ni-MH batteries are discussed as well.