Mg-ion storage materials based on MnO2 frameworks

Abstract

A wide variety of crystal structures for MNO2, so-called polymorphs, is promising for basic flameworks of cathode materials in next-generation batteries such as Mg rechargeable batteries (MRBs). In this short review, we summarize recent progress on MNO2-based cathode materials for MRBs, especially focusing on the structures of α-MnO2 and λ-MnO2 to discuss the criteria for achieving topotactic reactions during magnesiation. In contrast to adequately stable α-MnO2, spinel-structured λ-MnO2 is unstable at elevated temperatures around 150 °C; however, its stability can be significantly improved by materials design. Here we introduce as a successful example that defect spinel ZnMnO3 exhibits long-term cycle performance even at 150 °C with high potential and capacity.