Does the Mg–I₂ Battery Suffer Severe Shuttle Effect?
2018
Liu, Zhixiao | Pu, Xiong | Hu, Wangyu | Gao, Fei | Deng, Huiqiu
Metallic anodes in Li/Na–X (X = S, Se, I₂) 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–I₂ battery. Under the low-coverage condition (Θ = 12.5%), the Mg(0001) surface can provide strong chemical bonding interaction to the I₂ molecule, and the dissociation and reduction of I₂ 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 (Θ = 100%), and this layer excludes the rest of the I₂ molecules after the iodization. The ultrahigh iodine coverage (Θ = 200%) can also generate the partially iodized Mg surface which excludes I₂ 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 I₂ 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–I₂ battery.
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