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

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Magnesium rechargeable batteries are promising due to magnesium's high volumetric capacity.
• Magnesium bis(trifluoromethanesulfonyl) amide (Mg(TFSA)2) in triglyme (G3) electrolytes face anode passivation issues.
• TFSA anion reactivity is a critical challenge for practical magnesium battery applications.

Purpose of the Study:

• To investigate the effect of MgCl2 addition on Mg(TFSA)2/G3 electrolytes.
• To understand the suppression mechanism of Mg-metal anode passivation at elevated temperatures.
• To evaluate the electrochemical performance of a magnesium battery with the developed electrolyte.

Main Methods:

• Preparation of concentrated Mg(TFSA)2/G3 electrolytes with varying MgCl2 content.
• Electrochemical testing of Mg-metal anodes at elevated temperatures (around 150 °C).
• Fabrication and testing of a full cell using MgCo2O4 cathode and the optimized electrolyte.

Main Results:

• Addition of MgCl2 to concentrated Mg(TFSA)2/G3 solutions (1 ≤ G3/Mg-salts ≤ 2) at 150 °C significantly suppresses Mg-metal anode passivation.
• Decreasing G3 solvent content modifies Mg2+ solvation structure, lowering free TFSA anions and their reactivity.
• A full cell with Mg(TFSA)2/MgCl2/G3 (1:1:2) electrolyte at 150 °C achieved a stable cell voltage of ~2 V.

Conclusions:

• Concentrated Mg(TFSA)2/MgCl2/G3 electrolytes at high temperatures offer a viable solution to Mg-metal anode passivation.
• The modified solvation structure and reduced TFSA anion reactivity are key to improved battery performance.
• This research paves the way for developing high-performance magnesium rechargeable batteries.