Progress in nonaqueous magnesium electrochemistry

We report herein on recent studies related to nonaqueous magnesium electrochemistry and R&D of rechargeable magnesium batteries. Extensive attempts have been made to examine electrolyte systems based on ionic liquids as potential solutions for nonaqueous magnesium batteries. In general, magnesium electrodes are reactive with many imidazolium-based ionic liquids. In those liquids in which Mg electrodes are apparently stable, they develop a blocking passivation. It was possible to develop improved solutions for rechargeable magnesium batteries based on mixtures of THF, tetraglyme (where the high boiling point of the polyether improves the safety features), and complexes based on Lewis acid-Lewis base reactions between AlCl₂R and MgR₂ or RMgCl. The choice of the type of Lewis base, the R group and the appropriate acid-base ratios enables a reasonable specific conductivity to be obtained, 100% cycling efficiency of Mg electrodes, and a wide electrochemical window, up to 2.4 V. This work included rigorous studies by Raman spectroscopy, electron microscopy, ICP, and a variety of electrochemical techniques. In parallel, Mg insertion cathodes based on cubic TiS₂, NiS_x, NiSSe and CuS_x were also investigated.