The effect of Mg(ClO4)2 and HF acid in 1M LiPF6/EC+DEC+DME electrolyte on the cycle behaviors and the surface characteristics of the lithium electrode were investigated. The morphology of the electrode is greatly improved using Li–Mg co-deposition and HF acid, and results in the enhancement of the cyclability observed by electrochemical measurement. The scanning electron microscopy images of the electrode surface show densely deposited lithium–magnesium alloy particles with a hemispherical shape on the entire surface of the electrode. The improved coulombic efficiency was attributed to the synergistic effect due to the formation of Li–Mg alloy and LiF caused by Li–Mg co-deposition and HF to the electrolyte, respectively.