Polyanion-Based Compounds for Rechargeable Magnesium Batteries

Rechargeable magnesium metal batteries represent a compelling post-lithium energy storage technology owing to the abundance of terrestrial magnesium reserves, their current cost-effectiveness and intrinsically higher safety relative to lithium systems, coupled with their capacity to deliver high volumetric energy density. However, this promise and beyond remains constrained by the stringent requirement that rapid and reversible Mg 2+ transport can be achieved in concert with electrochemical and thermodynamic stability across both electrodes and electrolytes. Within this context, polyanion compounds, such as phosphates, silicates, and borates, have emerged as a pedagogically rich and technologically versatile class of materials. Polyanion-based compounds offer high redox voltages, exceptional thermal and chemical robustness, and a plethora of crystallographic chemistries that permit rational tuning of Mg 2+ migration pathways. This Review surveys polyanion-based positive electrodes and solid electrolytes for rechargeable magnesium batteries, with emphasis on computational prediction, mechanistic elucidation, synthetic methodology, advanced structural and spectroscopic characterisation, and the prospects for all- solid-state magnesium batteries capable of operating under high‑temperature conditions.