Challenges on Developing Room-Temperature Rechargeable Magnesium Batteries with Oxide Cathodes

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Constructing sustainable energy systems requires rechargeable batteries with high safety, long cycle life and low production costs. Rechargeable magnesium batteries (RMBs) have been expected to be a promising candidate owing to low resource constraints compared to the commercial Li-based batteries. However, the development of RMBs have been stagnated after the first report of a prototype system, which consists of a Chevrel phase cathode, Mo6S8, and a Cl-based electrolyte.[1] The development of high potential oxide cathodes and non-corrosion Cl-free electrolyte encounters significant difficulties. Specifically, for oxide cathodes, the strong Coulomb interaction between Mg2+ and host structures usually inhibits the solid-state diffusion, causing a significant low discharge capacity compared to the theoretical value and rapid capacity loss during cycling.[2] Besides, non-corrosion electrolytes usually passivate Mg metal anodes and/or induce side reactions on oxide cathodes,[3] where remarkably decreases the cell voltage and accelerates the decomposition of electrolytes and active materials.In this presentation, we introduce our efforts to construct room-temperature RMBs with oxide cathodes and Cl-free electrolytes combining both the experimental and computational approaches. To explore suitable host structures for the topotactic Mg2+ intercalation, we revealed the phase transformation pathways and evaluated cathode properties of various transition oxide cathodes (e.g. MnO2 polymorphs) at both elevated temperature (150℃) and room temperature.[3-6] Moreover, to assess the electrolyte compatibility, we discovered the connection between the solvation environment and the reaction behavior on both the oxide cathodes and Mg metal anodes.[3,7] These findings pave the way for room-temperature RMBs using oxide cathodes.[1] D. Aurbach et al, Nature 407, 724 (2000)[2] T. Ichitsubo et al, J. Mater. Chem. A 21, 11764 (2011)[3] X. Ye, H. Li, T. Ichitsubo et al, ACS Mater. Interfaces 14, 56685 (2022)[4] S. Okamoto, T. Ichitsubo et al, Adv. Sci. 2, 1500072 (2015)[5] K. Shimokawa, T. Ichitsubo et al, Adv. Mater. 33, 2007539 (2021)[6] T. Hayakeyama, H. Li, T. Ichitsubo et al, Chem. Mater. 33, 6983 (2021)[7] X. Ye, H. Li, T. Ichitsubo et al, submitted.