Solvation/Interface Tuning with Cl − ‐Mediated Passivation Suppression for MgCl 2 ‐Based Electrolytes

Magnesium‐ion batteries (MIBs) are promising candidates for next‐generation sustainable energy storage, featuring high theoretical energy density, low cost, and intrinsic safety. However, their practical application is severely limited by a long‐overlooked core bottleneck across non‐aqueous and aqueous electrolytes: Mg anode passivation and parasitic hydrogen evolution reaction (HER). This review innovatively integrates fragmented research, first systematically summarizing the common bottleneck of passivation/HER across different systems, while highlighting the unique dual synergistic role of Cl − (derived from MgCl 2 and its hydrate MgCl 2 ·6H 2 O): not only mitigating anode passivation via interfacial etching to break through the insulating film barrier but also optimizing solvation structures to fundamentally suppress parasitic reactions. We further emphasize the novel active water regulation strategy for aqueous systems (WIS, PEG‐modified, DESs) as a key breakthrough, outline remaining challenges, and propose a forward‐looking roadmap—offering a unified, innovative perspective to design high‐performance MgCl 2 ‐based electrolytes and expedite MIBs practicalization.