Regulating Electric Double Layer via Self‐Assembled Monolayer for Stable Solid/Electrolyte Interphase on Mg Metal Anode

Modulating the cationic solvation structure with high donor-number (DN) additive is an effective strategy to construct a stable solid electrolyte interphase (SEI) on the Mg anode, which necessitates meticulous consideration of electrolyte chemistry and substantial quantities of additives. Notably, the electric double layer (EDL) adjacent to anode is pivotal role in SEI formation yet remains understudied. In this study, we propose a novel self-assembled monolayer (SAM) strategy by utilizing (trifluoromethyl)trimethylsilane (TFTMS, only 2 vol %, 1.4 mol %, 0.135 mol L^-1), a low DN but strong Mg metal absorbability through electron-withdrawing groups(-CF₃), to modulate the complex structure of the Helmholtz absorption plane. Through dipole-dipole interaction between the electronegative fluorine (-CF₃ of TFTMS) and electropositive hydrogen (-CH₃/-CH₂ of solvents), TFTMS weakens solvent-Mg²⁺ coordination and thus enhances anion-Mg²⁺ interaction, inducing a stable and dense SEI with superior electronic insulation to realize horizontal Mg plating/stripping. Consequently, the designed electrolytes enable the symmetric cells to cycle stable for up to 1000 hours and reversible Mg plating/stripping under 5 mA cm^-2, they show favorable compatibility with various cathodes. More importantly, the SAM strategy has good generality in other electrolyte systems, demonstrating a simple and effective route to promote the practical application of rechargeable magnesium battery.