Fundamental insights into magnesium electrodeposition through operando X-ray diffraction: crystal growth, orientation evolution, and interfacial dynamics

Magnesium-ion batteries are promising candidates for next-generation energy storage owing to their high theoretical volumetric capacity and the natural abundance of magnesium. However, their development is limited by challenges in Mg plating and an incomplete understanding of interfacial processes at the metal anode. In particular, the structural evolution and growth mechanisms of electrochemically deposited Mg remain largely unexplored. This work employs in situ diffraction to investigate the dynamic evolution of the crystal structure and orientation during reversible magnesium deposition in three representative Mg electrolytes: all-phenyl complex (APC), Mg(NO₃)₂, and Mg(TFSI)₂ electrolytes. This approach enables real-time observation of electrochemically deposited Mg by correlating electrochemical controls with diffraction patterns. Key findings reveal that Mg deposition in the APC electrolyte initially and preferentially occurs at the (002) crystallographic plane, followed by subsequent growth along the (101) plane. In contrast, Mg deposition in the Mg(NO₃)₂ and Mg(TFSI)₂ electrolytes predominantly occurs at the (002) plane with notable differences in surface morphology and charge transfer resistance. Mg(NO₃)₂ forms a passivating layer that increases charge-transfer resistance, while Mg(TFSI)₂ leads to MgF₂ formation. These findings directly link Mg electrolyte chemistry and the interfacial structure of electrochemically deposited Mg and provide critical insights into the transformations that govern the performance of magnesium-ion batteries.