A Fluorinated Alkoxyaluminate Electrolyte for Magnesium-Ion Batteries

The lack of electrolytes that simultaneously possess high Coulombic efficiency, conductivity, and voltage stability has hindered the deployment of rechargeable magnesium-ion batteries. With few exceptions, the tenacious oxide layer on magnesium metal has limited the scope of research to halide ion-based electrolytes, which help activate the electrode surface but also limit the working voltage window considerably. Herein, we demonstrate a new class of magnesium electrolytes based on fluoroalkoxyaluminate anions synthesized via a facile and scalable method and its incorporation in a full battery cell. Mixtures of magnesium and aluminum fluoroalkoxides in ethereal solvents result in solutions that can reversibly deposit magnesium metal with near unit efficiency in addition to achieving suitable oxidative stabilities (>3.5 V vs Mg/Mg2+ on glassy carbon and gold) and conductivities (>6 mS cm–1).