A materials perspective on magnesium-ion-based solid-state electrolytes

As economically viable alternatives to lithium-ion batteries, magnesium-ion-based all-solid-state batteries have been researched to meet the criteria for an ideal energy storage device. With an energy-dense magnesium-metal anode, such batteries can provide almost double the volumetric energy density at half the cost when compared with that obtainable from the state-of-the-art lithium-ion batteries. Although the development of solid-state magnesium-based batteries is hindered by various factors, the identification of an appropriate electrolyte remains the most challenging and limiting factor. In this review, we provide a survey of inorganic ceramic, metal-organic framework, glass, and organic solid polymer electrolytes that have been developed till date. We discuss the relationship between the structure, composition, and ionic conductivity of these inorganic Mg 2+ -ion solid-state electrolytes as well as the fundamental Mg-ion conduction mechanisms that govern magnesium transport in these solids, emphasizing on Mg 2+ -ion-conducting inorganic materials. By a comparison of Mg 2+ - and Na + -ion conductors under the theoretical framework of multi-excitation entropy (or Meyer-Neldel rules), we highlight the possible differences between these two systems, which can yield substantially different ion transport characteristics. As economically viable alternatives to lithium-ion batteries, magnesium-ion-based all-solid-state batteries have been researched to meet the criteria for an ideal energy storage device.