High voltage cathode materials for rechargeable magnesium batteries: Structural aspects and electrochemical perspectives

• Comprehensive review of high-voltage cathode materials for rechargeable magnesium batteries. • Structural classification into 1D, 2D, and 3D Mg 2+ diffusion frameworks among transition metal oxides and polyanions. • Identification of key challenges including sluggish Mg 2+ diffusion, electrolyte incompatibility, and structural instability. • Emphasis on water content, pre-intercalation, and cut-off voltage as critical design factors for practical high-energy rechargeable magnesium batteries cathodes. Rechargeable magnesium batteries (RMBs) are a cutting-edge energy storage solution, with several advantages over the state-of-art lithium-ion batteries (LIBs). The use of magnesium (Mg) metal as an anode material provides a much higher gravimetric capacity compared to graphite, which is currently used as the anode material in LIBs. Despite the significant advances in electrolyte, the development of cathode material is limited to materials that operate at low average discharge voltage (<1.0 V vs. Mg/Mg 2+ ), and developing high voltage cathodes remains challenging. Only a few materials have been shown to intercalate Mg 2+ ions reversibly at high voltage. This review focuses on the structural aspects of cathode material that can operate at high voltage, including the Mg 2+ intercalation mechanism in relation to its electrochemical properties. The materials are categorized into transition metal oxides and polyanions and subcategorized by the intrinsic Mg 2+ diffusion path. This review also provides insights into the future development of each material, aiming to stimulate and guide researchers working in this field towards further advancements in high voltage cathodes.