Solvation Structure Regulation Coupled with Construction of Magnesiumophilic Interface for High‐Performance Mg‐Ion Batteries

Abstract Aqueous rechargeable magnesium ion batteries promise high energy density and safety but suffer from low cycling stability and poor reversibility, primarily due to side reactions and passivation resulting from the decomposition of free water. Here, the study proposes a novel electrolyte composed of cost‐effective MgCl 2 ∙6H 2 O and a strong polar aprotic solvent (N,N‐dimethylformamide, DMF). The stronger interaction between Mg 2+ and electronegative carbonyl oxygen in DMF induces the transformation of solvation structure from original [Mg(H 2 O) 6 ] 2+ to [Mg(H 2 O) 2 (DMF) 3 Cl] + , thus decreasing the coordination number of Mg 2+ ‐H 2 O from 5.7 to 1.571 and appropriately introducing Cl − to inhibit hydrogen evolution reactions (HER)/corrosion and regulate passivation layers. Furthermore, the construction of magnesiumophilic interface with a high HER over‐potential not only further suppresses the reactivity of active water but also realizes a stable under‐potential deposition (UPD) of Mg on the Zn substrate. Consequently, the symmetric cells with Zn substrate utilizing the MgCl 2 ∙6H 2 O‐DMF electrolyte can consistently cycle for over 5200 h with a low over‐potential of 80 mV at a current density of 0.2 mA·cm −2 , and the corresponding full cells exhibit a high discharge voltage that is 0.98 V higher than that of conventional aqueous systems.