Electrochemical Magnesium Deposition and Dissolution with High Efficiency in Ionic Liquid

We report for the first time that electrochemical magnesium deposition and dissolution on silver substrate with 100% cycling efficiency can be realized in the ionic liquid N-methyl-N-propylpiperidinium bis(trifiuoromethanesulfonyl)imide containing 1 M Mg(CF3SO3)2. Overpotential for the steady-state deposition-dissolution processes at 0.1 and 0.2 mA/cm2 is only several tens of millivolts against magnesium at room temperature. The cyclic voltammograms also demonstrated reversible magnesium steadystate deposition-dissolution around 0 V (vs Mg reference electrode). Impedance measurements of the electrode revealed a large electrochemical resistance during the initial Mg deposition. This resistance, however, became much smaller during steady-state cycling. Results from scanning electron microscopy showed that Mg deposition was not smooth and compact and could be completely dissolved electrochemically. The high reversibility of the electrochemical magnesium deposition and dissolution will promote the development of secondary magnesium batteries.