Toward Stable Multivalent Metal Batteries: Understanding the Interfacial Chemistry for Magnesium and Calcium Metal Anodes

ABSTRACT Metal anode batteries, particularly divalent systems including magnesium (Mg) and calcium (Ca), are promising candidates for next‐generation energy storage due to their high natural abundance and superior theoretical energy densities. However, the electrode/electrolyte interphase remains the paramount factor limiting the reversibility and reaction kinetics of Mg and Ca metal deposition/dissolution. Unlike the ionic‐conductive interphase demonstrated in monovalent metal (Li and Na) anode systems, conventional electrolytes often form ion‐insulating layers on the surface of Mg and Ca anodes, putting a significant barrier for reversible stripping and plating. This review provides a systematic analysis of recent advancements in understanding how the passivation layers impact Mg 2+ and Ca 2+ transport and reduction, and how these interphases evolve during electrochemical cycling. We also scrutinize the chemical composition and microstructures of the interphases in relation to electrolyte formulations. By establishing a correlation among electrolyte chemistry, interphase properties, and electrochemical performance for Mg and Ca metal anodes, this work provides a roadmap for the rational design of effective interphases for viable Mg and Ca metal batteries.