The electrodeposition of Mg metal from an ionic liquid-glyme mixture was investigated at room temperature. The mixture contains a glyme, a simple amide salt Mg(Tf 2 N) 2 (Tf = SO 2 CF 3), and a quaternary-ammonium Tf 2 N ionic liquid. Using the mixture bath, substantial cathodic electrodeposition of Mg at a large current density (∼10 mA cm −2) was observed, suggesting a change in coordination geometry around Mg 2+ cation together with improved conductivity. By mixing diglyme, the conductivity increased by an order of magnitude (2.5-2.6 mS cm −1) compared to the glyme-free ionic liquid (0.35 mS cm −1) and the viscosity became as low as that of pure glyme. Additionally, potentiostatic electrolysis resulted in a non-dendritic thin film of elemental Mg with metallic luster.

We prepared less volatile and halide-free electrolytes for room temperature non-dendritic magnesium (Mg) electrodeposition by mixing a Mg 2+ -amide-containing ionic liquid (IL) with equimolar glyme (Mg 2+ +IL : glyme = 1:1). Raman spectroscopy suggested that in the equimolar mixture most glyme molecules are coordinated to Mg 2+ cations and/or IL cations, which is also supported by a single crystal X-ray diffraction study. The glyme-coordinated IL electrolytes showed sizable redox currents (order of mA cm -2 ), while aging deterioration of electrochemical properties was observed for the triglyme mixture due to partial bath decomposition. The tetraglyme-coordinated IL electrolyte enabled flat electrodeposition of Mg with a metallic luster and showed with very high anodic stability (ca. +4 V vs. Mg) because of decrease in uncoordinated glymes, which can be used for high-voltage Mg ion batteries. In the last few decades elemental magnesium (Mg) has come to be viewed as one of the most interesting negative electrode materials for post lithium ion secondary batteries because of its high-theoretical capacity (3839 mAh cm -3 ), low electrode potential (-2.356 V vs. SHE), and natural abundance. The well-known electrolytes for electrodepositing Mg metal at room temperature are Grignard electrolytes comprised of an ether solvent tetrahydrofuran (THF) and alkylmagnesium halides RMgX (R = alkyl or aryl groups; X = Cl, Br). Addition of AlCl 3 makes more electroactive species of organo-halo-aluminates, giving larger current density and/or higher anodic stability.1-10 However, the highly volatile THF and the highly moisture sensitive RMgX and AlCl 3 are difficult to use practically. Safer alternatives to both solvents and solutes for Mg-ion battery electrolytes are still being sought.Several groups have reported deposition of elemental Mg without using THF or RMgX. Ionic liquids (ILs) are one of the least volatile solvents and efforts have been made to electrodeposit Mg from ILs. For example, Mg redox behavior has been observed in an IL solution of Mg(ClO 4 ) 2 or MgCl 2 , although their current densities were significantly lower than those for RMgX-dissolved ILs.11 Some organic solvents that enable redox of Mg are less volatile than THF; these include 2-methyl-tetrahydrofuran, 12 and ethyleneglycol dimethylethers (glymes), [13][14][15] where Mg halides and hydrides were dissolved. Notably, glymes have boiling points above 150• C and are relatively safe at room temperature. However, in halide or hydride solutions hazardous halogen gas or hydrogen gas may evolve through anodic oxidation. From this viewpoint amide electrolytes are quite desirable as they hardly yield dissociated halogen ions.Glyme solutions of magnesium amides such as bis [(trifluoromethyl) 16 Therefore, it is of special interest to investigate glyme-based electrolytes where all glymes coordinate to any cations such as metal cations and/or ammnonium cations of ILs. Notably, the reversible deposition/dissolution cycle of Mg was reported using Mg 2+ -amide-containi...

We explored tin (Sn) alloys (Cu-Sn, In-Sn, Pb-Sn) as possible candidates for negative electrode materials of magnesium ion secondary batteries. Cyclic voltammograms revealed that In-Sn, Pb-Sn, and elemental Sn are active against Mg insertion and desertion at room temperature in a Grignard reagent, while Cu-Sn intermetallics are considerably inactive. Moreover, more than ten times of reversible peak currents were obtained for In-Sn and Pb-Sn alloys compared to pure Sn, suggesting the low-melting-point alloys enable the faster diffusion of Mg2+ ions.

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