Anion-Regulated Solvation Structure and Electrode Interface toward Rechargeable Magnesium Batteries

Developing chlorine-free electrolytes enabling fast Mg²⁺ transport through a solid/cathode-electrolyte interphase (SEI/CEI) remains critical for rechargeable magnesium batteries (RMBs). However, single-anion electrolytes often lack the necessary redox properties for this requirement. Here, we propose a dual-anion electrolyte combining magnesium bis(trifluoromethanesulfonyl)imide and 1-butyl-1-methylpiperidinium trifluoromethylsulfonate (PP₁₄CF₃SO₃) in diglyme and 2-methoxyethylamine (MOEA) solvent, achieving efficient Mg plating/stripping, cathode compatibility, and high anodic stability. The electrostatic interactions between MOEA and Mg²⁺/CF₃SO₃^- stabilize the Mg-anode SEI while fostering C_xN_y-rich CEI formation. This leads to a significantly improved performance in Mg∥Mg and stainless steel (SS)∥Mg cells, with an extended lifespan over 2500 h and average Coulombic efficiency of 98.1%, respectively. Mo₆S₈∥Mg full cells exhibit excellent rate performance, while poly(6,6',6″-(benzene-1,3,5-triyl)tris(9,10-anthracenedione)) (PBAQ)∥Mg cells operate at 2.8 V (1 A g^-1) with ∼70% capacity retention after 200 cycles. The work highlights anion-mediated solvation regulation, providing insights into advanced electrolyte engineering in high-performance RMBs.