Dissolution Mechanism of Eutectic and Hypereutectic Mg-Sn Alloy Anodes for Magnesium Rechargeable Batteries

Magnesium rechargeable batteries (MRBs) are presently attracting much attention due to their low cost, high safety, and high theoretical volumetric capacity. Traditionally, pure magnesium metal has been used as an anode for MRBs, but its poor cycle performance, modest compatibility with conventional electrolytes, and sluggish kinetics limit the further development of MRBs. In this work, eutectic and hypereutectic Mg-Sn alloys were designed and studied as anodes for MRBs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results confirmed that these alloys contained unique microstructures consisting of α-Mg, Mg₂Sn, and eutectic phases. The dissolution processes of the Mg-Sn alloys were studied in an all-phenyl-complex (APC) electrolyte. A multiple-step electrochemical dissolution process and a special adsorption interface layer were established for the Mg-Sn alloy anodes with an eutectic phase. Hypereutectic alloys with mixed phases showed better battery performance than the eutectic alloy owing to their superior mechanical properties. In addition, the morphology and Mg dissolution mechanism of the Mg-Sn alloys during the 1^st dissolution process were characterized and discussed.