Spinel-rocksalt transition as a key cathode reaction toward high-energy-density magnesium rechargeable batteries

Mg-metal-anode rechargeable battery (MRB) has been a promising candidate for next-generation batteries with high energy densities and high safety. The lack of high-performance cathode materials, however, retards the development of MRBs. In recent years, it has been revealed that various spine! oxides can accommodate a large amount of Mg, exhibiting relatively high potentials (2-3 V vs. Mg2+/Mg) and high capacities (similar to 150 mAh g(-1)) accompanied by the coherent structural transformation into the rocksalt structure. This review summarizes the recent progress in the development of such spinel-rocksalt transition materials from the viewpoints of the reaction mechanisms, design guidelines of spine! oxides (for tailoring the redox potential, volume change, and cyclability), and challenges to construct full-cell MRBs.