Recent Advances in Magnesium Battery Chemistry: Electrolyte–Electrolyte‐Derived Active Ion Species as the Key to Interfacial Performance

Rechargeable magnesium‐ion batteries (MIBs) have garnered significant attention due to their high theoretical energy density and favorable safety profiles. However, their practical application is still hindered by critical interfacial challenges, i.e., passivation of the magnesium metal anode and sluggish Mg 2+ intercalation kinetics in the cathode. Fundamentally, these issues stem from the substantial differences in chemical properties of active ion species (e.g., [MgCl] + , [Mg·solvent n ] 2+ ) across various electrolyte systems, which directly govern the Mg migration capability within electrode, alternating the deposition/intercalation reactions. This review systematically summarizes the mechanisms by which characteristic ion components in diverse electrolytes (i.e., Cl‐containing complexes, weakly coordinating anion electrolytes, aqueous electrolytes, and emerging solid‐state systems) regulate the thermodynamics and kinetics of interfacial reactions at both the anode and cathode. This review critically deconstructs the persistent gap between the practical performance of Mg‐ion batteries and their theoretical targets of >2.5 V and 300 mAh g −1 . Moving beyond a simple catalog of advances, we diagnose the fundamental electrochemical hurdles and propose targeted electrolyte and interfacial engineering strategies as synergistic solutions. Moreover, we advocate for standardized testing to build reliable data. Overall, this review links diagnostics with solutions to guide the rational design of high‐performance MIBs.