Magnesium and Calcium Batteries: Fundamental Challenges and Materials Exploration

Rechargeable magnesium (Mg) and calcium (Ca) batteries based on multielectron redox charge storage mechanisms promise high theoretical energy densities and enhanced safety for next- generation sustainable energy storage. The key challenge in developing divalent metal batteries arises from the intrinsic nature of divalent working ions, which determines their battery chemistries and limits the direct adoption of material design strategies from monovalent lithium- and sodium-ion systems. Herein, we will discuss the unique chemistries and recent advancements of Mg- and Ca-ion electrolytes. We will also present the recent progress in the search of suitable electrode materials for divalent metal batteries, with a focus on sulfur- and organic-based cathodes as well as alloy anodes.