Magnesium dendrite growth during electrodeposition in conditioned Mg(TFSI)2/AlCl3/MgCl2/DME electrolyte

Mg-ion batteries (MIBs) have emerged as a promising alternative to Li-ion batteries (LIBs) since Mg metal is more abundant, cheaper, and safer than Li metal. However, the growth of Mg dendrites on metal Mg anodes is still very controversial, while several studies claim that Mg dendrites do not form on Mg metal anodes; other studies claim the opposite. Recently, a new class of MIB electrolytes which we refer to here as MACT has received extensive attention due to its higher ionic conductivity and wider potential window. MACT is made of magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2), aluminum chloride (AlCl3), and magnesium chloride (MgCl2) in 1,2-dimethoxyethane (DME). Previous studies have claimed that Mg dendrites do not grow in conditioned MACT electrolytes. This article explores the formation of magnesium (Mg) dendrites in a conditioned MACT electrolyte during electrodeposition. A symmetric cell configuration, Mg|MACT|Mg, was utilized to investigate the dendrite formation at different current densities. The morphology, chemical composition, and crystal structure of the deposition products were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Our findings demonstrate the growth of Mg dendrites within the MACT electrolyte. We observed that the morphology of these dendrites undergoes evolution with varying the electrodeposition current density, transitioning between mossy clusters, granular structures, and porous mesh formations in a size range from approximately 10 to 125 μm. These results significantly enhance our understanding of Mg dendrite formation in MIBs.