Ionic liquid/tetraglyme hybrid Mg[TFSI]2 electrolytes for rechargeable Mg batteries

Abstract

The electrochemical reversibility of Mg in hybrid electrolytes based on mixtures of ionic liquid and glyme based organic solvents was investigated for applications in rechargeable magnesium batteries (RMBs). The electrolytes demonstrate reversible reduction and oxidation of Mg only after being pre-treated with the dehydrating agent, magnesium borohydride, Mg[BH4]2, highlighting the importance of removing water in Mg based electrolytes. The addition magnesium di[bis(trifluoromethanesulfonyl)imide] (Mg[TFSI]2) (0.3 M) to N-butyl-n-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide [C4mpyr][TFSI]/tetraglyme at a mole ratio of 1:2 showed stable CV cycling over almost 300 cycles while scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirmed Mg deposition, showing non-dendritic morphology and a well-aligned growth. Further thermogravimetric analysis (TGA) demonstrated a mass retention of 79% at 250 °C for this electrolyte suggesting that the presence of the ionic liquid increases thermal stability substantially making these hybrid electrolytes compatible for RMBs. Keywords: Mg[TFSI]2, Ionic liquids, Tetraglyme, Rechargeable Mg battery, Mg[BH4]2 dehydrate reagent