Solvation-Structure Modification by Concentrating Mg(TFSA)-MgCl-Triglyme Ternary Electrolyte.

Mg(TFSA)/triglyme(G3)-based electrolytes (TFSA: bis (trifluoromethanesulfonyl) amide) are one of candidates for magnesium rechargeable batteries, but the passivation of Mg-metal anode due to the TFSA anion is fatal in practical use. In this work we show that at elevated temperatures around 150 °C a comparable amount of MgCl salt can be dissolved in concentrated Mg(TFSA)/G3 solutions, and the passivation of Mg metal is markedly suppressed in such highly concentrated solutions (1 ≤ G3/Mg-salts ≤ 2) in comparison with in the dilute solutions (G3/Mg-salts ≫ 2). By decreasing the amount of G3 solvent, the solvation structure of Mg ions is modified in that free TFSA anions are drastically lowered, which would consequently decrease the reactivity of TFSA anions. We also demonstrate that a full-cell using MgCoO cathode with the electrolyte of Mg(TFSA)/MgCl/G3 1:1:2 at 150 °C delivers a cell voltage of ∼2 V versus Mg-metal anode.