An Efficient Bulky Mg[B(Otfe)₄]₂ Electrolyte and Its Derivatively General Design Strategy for Rechargeable Magnesium Batteries

The requirement of practical high-performance electrolytes is a key bottleneck restricting the development of rechargeable magnesium batteries (RMBs). Electrolytes based on weakly coordinated and fluorinated bulky boron-center anions (B(ORF)4–) have attracted wide attention for their admirable oxidation stability, high ionic conductivity, and weak corrosion. However, the complex synthesis route and costly raw materials still hinder their wide application. Therefore, a magnesium tetra(trifluoroethanoloxy)borate (Mg[B(Otfe)4]2) is designed not only to inherit these merits above but also greatly cut down the synthetic costs. The as-prepared electrolyte is synthesized by two methods of microcrystal redissolution and in situ reaction, both of them cycle stably for reversible Mg plating–stripping with an average Coulombic efficiency of ∼99% and overpotentials as low as 0.2 V, as well as an oxidation stability of more than 3 V vs Mg at stainless steel. The design strategy of the electrolyte and its compatibility with insertion or replacement-type cathodes promote the realization of practical RMBs.