Uniform and Dense Electrodeposited Magnesium Foil Induced by Cationic Surfactant Additive as an Ultra‐Thin and High‐Utilization Negative Electrode for Rechargeable Magnesium Batteries

ABSTRACT Rechargeable magnesium batteries (RMBs) have garnered significant attention due to the high theoretical capacity (3833 mAh cm −3 ) and abundant resources of magnesium negative electrode. The preparation of high‐performance ultrathin magnesium foil negative electrode is crucial for achieving high‐energy‐density magnesium batteries. Electrodeposition has proven to be an effective method for producing ultrathin magnesium foil, but the uniformity and density of electrodeposited magnesium foil still need to be further optimized. This study systematically screens long‐chain quaternary ammonium salt as electrodeposition additives and discovers that cetyltrimethylammonium bromide (CTAB) effectively induces the formation of magnesium deposits with lower surface roughness and higher structural density. Combining density functional theory calculations and systematic experimental characterizations, the mechanism of CTAB additive is demonstrated as that CTA + ions adsorb at the electrode interface to regulate the magnesium nucleation‐growth process, thereby achieving more uniform deposition morphology. The optimized magnesium negative electrode delivers a cycle life of 500 h at 5 mA cm −2 and 5 mAh cm −2 (83.3% utilization rate) with an overpotential of only 0.18 V, and the Mg||Mo 6 S 8 full cell maintains a capacity of 79.1 mAh g −1 after 500 cycles. This study provides a pathway for designing and fabricating high‐utilization, long‐cycle‐life magnesium metal negative electrode.