Dendrite Growth in Mg Metal Cells Containing Mg(TFSI)2/Glyme Electrolytes

One advantage of Mg batteries, which is often reported in the literature without further qualification such as the electrolyte system, is the high safety due to dendrite-free Mg deposition. Here we report results of a study on the possibility for dendrite growth in Mg metal cells using Mg(TFSI)2/glyme electrolytes. Dendrite growth and the subsequent internal short-circuit were proven electrochemically via cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and galvanostatic cycling. In addition, the structure and chemical composition of the globular dendrites were investigated by scanning electrode microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and in situ optical microscopy. The dendrites are structured in interconnected spherical deposits consisting of Mg metal, MgO, MgF2, and MgS. The results demonstrate the necessity of considering dendrite growth when developing new electrolyte systems for Mg metal batteries.