A covalent organic framework protection layer for highly active and stable Mg metal anode toward magnesium–sulfur batteries

Magnesium–sulfur (Mg–S) batteries exhibit advantages of abundant material resources and admirable theoretical energy density. However, their application is hindered by severe dissolution of polysulfide species from the cathode, which causes the passivation of the Mg metal anode and the subsequent battery failure. Herein, a covalent organic framework (COF) layer was coated on a magnesium foil (Mg@COF), which achieves significantly enhanced redox currents of magnesium deposition/dissolution in the asymmetric Cu–Mg cell. The as-prepared Mg@COF anodes demonstrate a long cycling stability of up to 1300 h (∼5.3 times higher than that of the bare Mg metal anode) in the symmetric Mg–Mg cell. When the Mg@COF is employed in an Mg–S battery, a reversible capacity of 245.1 mAh/g for the sulfur cathode remains after 50 cycles. In contrast, the battery failure occurs after 11 cycles using the bare Mg metal anode.