Uniform nanoplating of metallic magnesium film on titanium dioxide nanotubes as a skeleton for reversible Na metal anode

To meet the low-cost concept advocated by the sodium metal anode, this paper reports the use of a pulsed electrodeposition technology with ionic liquids as electrolytes to achieve uniform nanoplating of metallic magnesium films at around 20 nm on spaced titanium dioxide (TiO₂) nanotubes (STNA-Mg). First, the sodiophilic magnesium metal coating can effectively reduce the nucleation overpotential of sodium metal. Moreover, three-dimensional STNA can limit the volume expansion during sodium metal plating and stripping to achieve the ultrastable deposition and stripping of sodium metals with a high Coulombic efficiency of up to 99.5% and a small voltage polarization of 5 mV in symmetric Na∥Na batteries. In addition, the comparative study of sodium metal deposition behavior of STNA-Mg and STNA-Cu prepared by the same route further confirmed the advantage of magnesium metal to guide sodium metal growth. Finally, the prepared STNA-Mg–Na metal anode and commercial sodium vanadium phosphate cathode were assembled into a full cell, delivering a discharge capacity of 110.2 mAh·g⁻¹ with a retention rate of 95.6% after 110 cycles at 1C rate.