Perfluorinated Asymmetric Magnesium Salts Enable Stable and Dendrite‐Free Magnesium Batteries

ABSTRACT

Rechargeable magnesium batteries face instability and irregular deposition, which lead to dendritic growth, low Coulombic efficiency, and poor cycle life. In this study, we propose a perfluorinated asymmetric magnesium salt (Mg(PFBS) ₂ ) to regulate magnesium‐ion deposition and improve interfacial stability. The PFBS ^–  anion tailors the solvation structure and optimizes the electric double layer (EDL), promoting Mg ²⁺ desolvation and suppressing solvent decomposition. Based on diffusion‐controlled theory, we introduce Damköhler (Da) and Wagner (Wa) numbers to elucidate the competition between electrochemical reaction kinetics and atomic/ionic diffusion governing Mg deposition behavior. Experimental and theoretical analyses indicate that PFBS ⁻ preferentially adsorbs on the Mg(002) plane, forming a Mg‐PFBS ⁻ interfacial layer that induces epitaxial growth dominated by Mg(002) orientation, significantly improving deposition uniformity. The strong electron‐withdrawing perfluorinated structure further enables preferential anion reduction, forming an inorganic‐rich, dense, and stable solid electrolyte interphase (SEI). Electrochemical measurements demonstrate that Mg||Mg symmetric cells maintain stable cycling for over 1800 h at 0.1 mA cm ⁻² and 0.05 mAh cm ⁻² , with an average Coulombic efficiency of 99.47%. Furthermore, Mg||Mo ₆ S ₈ full cells exhibit superior rate capability and long‐term cycling stability, retaining 88.6% capacity after 380 cycles at 1 C. This study offers an effective electrolyte design strategy high‐energy‐density and safe magnesium batteries.