The challenge of developing rechargeable magnesium batteries

The high specific capacity, reactivity, and abundance of magnesium in the earth's crust and the relatively good safety features of Mg metal, despite its being a reactive metal, drive intensive efforts to develop rechargeable Mg batteries as a follow-up to the success of Li-ion battery technology. However, Mg anodes cannot function in usual non-aqueous electrolyte solutions. Consequently, it is important to develop unique, complex solutions for reversible Mg metal anodes. Also, finding relevant cathode materials that can reversibly insert bivalent Mg ions is a great challenge. In this article, we review the efforts and success in the development of several families of electrolyte solutions for secondary Mg batteries, in which Mg anodes behave fully reversibly, but also exhibit the necessary wide electrochemical window. We also review attempts to develop positive electrodes for rechargeable Mg batteries. The first generation of secondary Mg batteries has already been demonstrated, but their specific energy density remains relatively low. The challenge now is to develop novel Mg battery prototypes that possess high energy density.