Sulfone-Based Electrolyte Solutions for Rechargeable Magnesium Batteries Using 2,5-Dimethoxy-1,4-benzoquinone Positive Electrode

of which are solid at room temperature, were used as received, and EiPS was dehydrated by immersing metallic magnesium flakes (Aldrich) before preparation of the electrolyte solution. The water contents of SL, EiPS and DnPS, determined using a Karl-Fischer coulometer Model 831 (Metrohm), were 117(3), 133(10) and 50(4) ppm, respectively (average of three runs (standard deviation)). The solute, magnesium bis(trifluoromethanesulfonyl)amide (Mg(TFSA)2, Kishida Chemical, 99%, water content <0.1%), was used without further purification. The electrolyte solutions were prepared by dis- solving 0.5 mol L −1 Mg(TFSA)2 in each sulfone with heating. The water contents of the electrolyte solutions of SL, EiPS and DnPS were 228(4), 398(6) and 62(8) ppm, respectively. 2,5-Dimethoxy-1,4-benzoquinone(DMBQ),thepositiveelectrode active material, was purchased from Tokyo Chemical Industry (98%, Particle size: 40 ± 5 μm) and used as received. Magnesium ribbons (Nilaco, t 0.24 mm × d 3.2 mm, 99.9 wt%) and wires (Japan Fine Steel, ϕ 0.5 mm, 99.95 wt%) were used as the negative and reference electrodes, respectively. Prior to the electrochemical measurements, they were polished with an alumina lapping film (#600, 3M). All the experimental procedures were conducted in a dry-box or an Ar-filled glove-box, in which the dew point was maintained below -63 and -78 ◦ C, respectively.