Effect of EtOMgCl Salt to Suppress Reductive Decomposition of TFSI⁻ Anion in Electrolyte for Magnesium Rechargeable Battery

Abstract

The relationship between reductive decomposition of anion and the efficiency of magnesium deposition was investigated in magnesium bis (trifluoromethane sulfonyl) imide (Mg(TFSI)2) salt and triglyme (G3) solvent without and with magnesium ethoxy chloride (EtOMgCl) salt. Cyclic voltammetry, energy dispersive X-ray spectroscopy analysis, in situ infrared spectroscopy during deposition-dissolution of magnesium and Raman spectroscopy were conducted. Coulombic efficiency for magnesium deposition was also calculated by chrono amperometry. In Mg(TFSI)2/G3 (molar ratio of 1/15), magnesium was hardly deposited. In EtOMgCl/Mg(TFSI)2/G3 (molar ratio of 2/1/15), magnesium was deposited efficiently. The reduction of TFSIanion occurred in Mg(TFSI)2/G3 during magnesium deposition, while the reduction was suppressed in EtOMgCl/Mg(TFSI)2/G3. The addition of EtOMgCl salt can suppress the reduction of TFSIanion, leading to highly efficient magnesium deposition.

Triiodide Anion as a Magnesium-ion Transporter for Low Overpotential Battery Cycling in Iodine-Containing Mg(TFSI)2 Electrolyte

“…After 10 scans, we observe a significant loss in current density, as expected with the growth of a passivating layer resulting from known electrolyte TFSI − decomposition. 24,28,29,33,34 Figure 5b shows that by adding the MgI 2 SEI ex situ, the onset potential for Mg stripping does not increase, while the onset potential for deposition does decrease over 10 scans, and there remains a decrease in current density after 10 scans. Figure 5c shows that after adding 5 mM I 2 to the Mg(TFSI) 2 electrolyte, a decrease in the onset potential for Mg deposition (from ∼−0.3 to ∼−0.2 V for the first scan, from ∼−1.2 to −0.1 V for the 10th scan) and stripping (from ∼0.6 to ∼0.4 V for the first scan, from ∼0.9 to ∼0.1 V for the 10th scan) is observed when compared to cells with no additive.…”