Constructing ultra-thin magnesium foil by electrolysis as a stable and high-utilization negative electrode for rechargeable magnesium battery

Rechargeable magnesium batteries (RMBs) have attracted much attention due to the high theoretical capacity (3833 mAh cm⁻³) of magnesium metal negative electrode and abundant resources. However, the preparation of ultra-thin magnesium foils faces the problems of rolling difficulty and high processing cost, while the use of thick magnesium foils leads to low utilization of magnesium and reduces the energy density. To tackle the above problems, we successfully prepared ultra-thin magnesium foils based on electrolytic process and investigated the effect of different substrates. The magnesium foils prepared using Mo substrate have more uniform surface morphology and lower surface roughness, which is attributed to the lower magnesium nucleation overpotential of Mo substrate. Meanwhile, density functional theory calculations show that the adsorption energy of Mo on Mg is more negative, which is conducive to achieving uniform nucleation and deposition of Mg. The Mg deposition on Mo substrate undergoes the characteristic stages of transient nucleation, nucleus accretion, multidirectional heterotopic growth, and columnar crystal stacking, and ultimately the formation of a dense deposited layer. In addition, the prepared ultra-thin Mg foil with Mo substrate can stably cycle for 1000 h at 3 mA cm⁻² with high utilization of 50% in the symmetric cell. This study develops a facile method for the preparation of ultra-thin Mg foils, which opens up a new path for developing high-performance ultra-thin negative electrodes for RMBs.