Novel Design Concepts of Efficient Mg-Ion Electrolytes toward High-Performance Magnesium-Selenium and Magnesium-Sulfur Batteries

Developing high-voltage Mg-compatible electrolytes (>3.0V vs Mg) still remains to be the biggest R&D challenge in the area of nonaqueous rechargeable Mg batteries. Here, the key design concepts toward exploring new boron-based Mg salts in a specific way of highlighting the implications of anions are proposed for the first time. The well-defined boron-centered anion-based magnesium electrolyte (BCM electrolyte) is successfully presented by facile one-step mixing of tris(2H-hexafluoroisopropyl) borate and MgF2 in 1,2-dimethoxyethane, in which the structures of anions have been thoroughly investigated via mass spectrometry accompanied by NMR and Raman spectra. The first all-round practical BCM electrolyte fulfills all requirements of easy synthesis, high ionic conductivity, wide potential window (3.5 V vs Mg), compatibility with electrophilic sulfur, and simultaneously noncorrosivity to coin cell assemblies. When utilizing the BCM electrolyte, the fast-kinetics selenium/carbon (Se/C) cathode achieves the best rate capability and the sulfur/carbon (S/C) cathode exhibits an impressive prolonged cycle life than previously published reports. The BCM electrolyte offers the most promising avenue to eliminate the major roadblocks on the way to high-voltage Mg batteries and the design concepts can shed light on future exploration directions toward high-voltage Mg-compatible electrolytes.