A Simple Mg(SO3CF3)2-Based Electrolyte with Additive of 2-Methoxyethylamine for Performance Enhancement in Rechargeable Magnesium–Sulfur Batteries

Abstract The exploration of low-cost, environment-friendly and high-performance electrolytes play a pivotal role in the commercial application process of the rechargeable magnesium batteries (RMBs). Here, we successfully prepared a simple Mg(CF3SO3)2-based electrolyte for RMBs through introducing the nitrogenous co-solvent 2-methoxyethylamine (MOEA) with high Gutmann donor number (DN) for competing solvation coordination into the Mg(CF3SO3)2–MgCl2/DME electrolyte. As a result, the addition of the co-solvent MOEA effectively ameliorate the reversible Mg plating-stripping performance in Mg(CF3SO3)2–MgCl2/DME electrolyte. Upon the volume ratio of MOEA to DME being equal to 1:6, the as-prepared electrolyte exhibits the superior Mg plating-stripping performances, such as passable oxidative stability of 2.5 V (SS, vs Mg/Mg2+), moderate ionic conductivity of 1.27 mS cm–1 and CE values above 92.3%, low overpotential of 70 mV (vs Mg/Mg2+), and long cycling stability of over 500 h. The co-solvent MOEA can improve the bulk performance of the Mg(CF3SO3)2–MgCl2/DME electrolyte by regulating the solvation structure of Mg2+, accelerating the formation of SEI on the Mg anode and suppressing the oxidative decomposition of Mg(CF3SO3)2. Surface analysis of the Mg anode reveals the formation of a uniform layer of nanoparticles distributed across the Mg anode surface, which is favorable to the stable and long-term Mg plating-stripping cycling process. The prime active species in the electrolyte are identified as tetrahedron anions CF3SO3– and solvated cations [Mg2(μ-Cl)2(DME)2(MOEA)2]2+. Additionally, the full cell configurations using a Chevrel phase Mo6S8, a CuS cathode, and a S-CNT cathode show average discharge specific capacities of 75, 198, and 890 mAh g–1 at 0.1 C, with capacity retention rates of above 97%, 40%, and 72% after 40 cycles, respectively, indicating the decent compatibility of this electrolyte with the sulfur-containing cathodes. This work convincingly offers a rational strategy to develop non-nucleophilic electrolyte which is a potential candidate for the practical application of Mg/S batteries.