Moving toward high‐energy rechargeable Mg batteries: Status and challenges

Lithium-ion batteries (LIBs) have gained significant market share in the field of consumer electronics, grid storage, and hybrid electric vehicles, because of its exceptional energy densities per unit volume (area or weight) compared to other electrochemical energy storage systems. However, they do approach its maximum practical capacities and efforts are underway to explore future battery systems with enhanced energy density than LIBs. There has been growing interest in incorporating multivalent ions such as Zn2+, Mg2+, and Al3+, since they offer greater volumetric energy densities than its monovalent counterparts like LIBs and sodium-ion batteries. It has long been acknowledged that replacing lithium with magnesium (Mg) ions in battery systems has many potential benefits such as low cost, excellent rate capability, high energy density, ease of handling, and eco-friendly. Yet, a few breakthroughs has been made in the advancement of rechargeable magnesium batteries (RMBs) since its first discovery in 2000. The success of RMBs has been hindered by the slow electrode kinetics and also the formation of passive layers on Mg metal surfaces seriously affecting its performance during Mg2+ ion magnesiation/de-magnesiation. This chapter provides comprehensive knowledge on the background of rechargeable Mg batteries, principles, and cell configuration, discussing key advancements made in the last two decades in terms of its electrode materials and electrolytes. Finally, a brief note on future research strategies is outlined. Highlights Mg-ion batteries may replace Li-ion batteries to meet the demands of both consumer and industrial energy storage. Recent progress on the anode, cathode, and electrolytes for Mg-ion batteries is reviewed. The importance of chemical and structural details on the energy storage performance is emphasized. A brief overview of the electrochemical performance of different anodes, cathodes, and electrolytes has been discussed.