Dual-functional CF3SO3−/amine additives synergistically construct an MgF2/Mg3N2-rich interphase toward high-performance magnesium–sulfur batteries

Abstract

Exploring promising non-nucleophilic electrolyte systems that enable reversible and efficient Mg plating/stripping while maintaining excellent stability represents a critical advancement for practical magnesium–sulfur (Mg/S) batteries. Herein, we designed an innovative mononuclear non-nucleophilic electrolyte by strategically incorporating trifluorosulfonate anions (OTf⁻) and (S)-1-methoxy-2-propylamine (M4) additives into an Mg(AlCl₄)₂/PYR14TFSI/DME (designated as MAID) electrolyte. The resulting [Mg(M4)₃(OTf)]⁺ coordination complex exhibited a reduced LUMO energy level that promoted the in situ formation of an MgF₂/Mg₃N₂-rich solid-electrolyte interphase on an Mg anode. This tailored interphase not only facilitated Mg²⁺ transport kinetics but also established a stable interface that persistently suppressed parasitic reactions. Consequently, the MAID-NaOTf-M4 electrolyte exhibited exceptional Mg plating/stripping reversibility with minimal polarization below 200 mV for over 1600 h of cycling at 0.1 mA cm⁻², high anodic stability up to 3.4 V vs. Mg/Mg²⁺, superior rate capability, high ionic conductivity of 8.45 mS cm⁻¹ and a coulombic efficiency of 97.0% sustained over 1000 cycles. Notably, its non-nucleophilic nature ensured compatibility with sulfur-based cathodes, enabling the assembled Mg‖CMK-3@S_0.86Se_0.14 full cells to deliver outstanding rate performance and exceptional cycling stability, with capacities of 675.2 mAh g⁻¹ retained after 200 cycles at 0.1C and 302.1 mAh g⁻¹ after 400 cycles at 0.5C, along with ∼100% coulombic efficiency. This work provides valuable insights for the rational design of advanced electrolytes that concurrently optimize solvation structures and interfacial architecture to achieve high-performance Mg/S batteries.