Solid-State Electrolytes for Rechargeable Magnesium-Ion Batteries: From Structure to Mechanism

Rechargeable magnesium (Mg)-ion batteries have received growing attention as a next-generation battery system owing to their advantages of sufficient reserves, lower cost, better safety, and higher volumetric energy density than lithium-ion batteries. However, Mg as an anode can be easily passivated during charging/discharging by most common solvents, which are inconducive for magnesium deposition/stripping. Based on this, the development of Mg-ion solid-state electrolytes in the last decades led to the formulization of several concepts beyond previously reported designs. These exciting studies have once again sparked an interest in all-solid-state magnesium-ion batteries. In this review, Mg solid-state electrolytes, including inorganic (oxides, hydrides, and chalcogenides) and organic (metal-organic frameworks and polymers) materials are classified and summarized in detail. Moreover, the structural characteristics and the migration mechanism of Mg²⁺ ions are also discussed with a focus on pending questions and future prospects.