Does the Mg-I2 Battery Suffer Severe Shuttle Effect?

Metallic anodes in Li/Na-X (X = S, Se, I-2) batteries, in which the working mechanism is a conversion reaction, suffer severe corrosion and self-discharge caused by the shuttle effect. Beyond alkali metals, magnesium is also considered as the next-generation metallic anode for secondary batteries. The present study used atomic-scale modeling strategies to reveal the iodization reaction on the anode surface in the Mg-I-2 battery. Under the low-coverage condition (Theta = 12.5%), the Mg(0001) surface can provide strong chemical bonding interaction to the I-2 molecule, and the dissociation and reduction of I-2 to I- anions are thermodynamically and kinetically preferred. Ab initio molecular dynamics simulations demonstrate that a partially iodized layer forms on the anode surface under the high iodine coverage condition (Theta = 100%), and this layer excludes the rest of the I-2 molecules after the iodization. The ultrahigh iodine coverage (Theta = 200%) can also generate the partially iodized Mg surface which excludes I, molecules. However, the ultrahigh coverage also results in great surface reconstruction, which potentially leads to the loss of Mg. According to the present simulation, Mg(NO3)(2) is helpful for forming a thin and robust magnesium oxynitride protecting layer on the fresh Mg anode. This protecting layer can block the interaction between the Mg anode and I-2 shuttled from the cathode side. The present theoretical study reveals that the Mg anode shows good resistance to iodization-induced corrosion and self-discharge, and the Mg(NO3)(2) treatment can further improve the performance of the metallic anode in the Mg-I-2 battery.