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

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 TFSI⁻ anion 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 TFSI⁻ anion, leading to highly efficient magnesium deposition.