Solvation-Structure Modification by Concentrating Mg(TFSA)2–MgCl2–Triglyme Ternary Electrolyte

• Published in: The journal of physical chemistry letters 2018-08, Vol.9 (16), p.4732-4737
• Main Authors: Shimokawa, Kohei, Matsumoto, Hajime, Ichitsubo, Tetsu
• Format: Article
• Language: English
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.8b02209

Mg­(TFSA)2/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 MgCl2 salt can be dissolved in concentrated Mg­(TFSA)2/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 Mg2+ 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 MgCo2O4 cathode with the electrolyte of Mg­(TFSA)2/MgCl2/G3 1:1:2 at 150 °C delivers a cell voltage of ∼2 V versus Mg-metal anode.