Electrochemical Deposition and Dissolution Behavior of Magnesium Metal in Organosilicon-Containing Electrolyte Solutions

Abstract

Introduction: Magnesium metal rechargeable batteries are expected as post lithium-ion batteries. One of the drawbacks of the development of magnesium metal rechargeable batteries is electrolyte. Research for electrolyte has been investigated extensively. We also reported the magnesium(II) bis(trifluoromethanesulfony)amide (Mg(TFSA)2)/triethylene glycol dimethyl ether (triglyme) that enabled magnesium metal to deposit/dissolve at ambient temperature[1]. However, low coulombic efficiency and large over potential should be overcome. In this study, fluoroorganosilicon compound (FOS) that has high electrochemical and thermal stability was used as co-solvent to overcome these issues. Electrochemical deposition and dissolution behavior of magnesium metal in the Mg(TFSA)2/ triglyme+FOS was investigated. Experimental: A three-electrode cell was used. Platinum plate was used as a working electrode and magnesium wires were used as a counter electrode and a quansi-reference electrode. 0.5 mol dm-3 Mg(TFSA)2/triglyme+FOS(various ratio) was used as electrolyte solutions. Cyclic voltammetry and chronopotentiometry measurement was carried out. X-ray diffraction (XRD) measurement and scanning electron microscope (SEM) observation were conducted. All operations and electrochemical measurements were carried out in Ar-filled glove box. Results and discussion: Figure 1 shows the cyclic voltammograms of the Pt electrode in Mg(TFSA)2/triglyme and Mg(TFSA)2/triglyme+FOS (1:2 by vol.) at the 5th cycle. Both reduction and oxidation currents were observed at the potential around - 2 V and 1 V, respectively. After chronopotentiometry, magnesium metal deposition was confirmed by XRD pattern and SEM image. Coulombic efficiency in triglyme+FOS was higher than that in triglyme. Based on this result, it is suggested that the addition of FOS is effective to magnesium metal deposition and dissolution reaction in triglyme. Reference: 1. T. Fukutsuka, K. Asaka, A. Inoo, R. Yasui, K. Miyazaki, T. Abe, K. Nishio and Y. Uchimoto, Chem. Lett., 11 (2014) 1788. Figure 1