The quest for new electrolyte and cathode materials is a crucial point for beyond-lithium-ion energy storage systems. Following this, an electrolyte for secondary magnesium batteries based on a new iodoaluminate ionic liquid and delta-MgI2 is reported. Promising electrochemical performance in terms of Mg plating-stripping, coulombic efficiency, and conductivity, demonstrates the potential of this iodine-based system for future Mg secondary batteries.