Does the Mg–I₂ Battery Suffer Severe Shuttle Effect?

Abstract

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.

Rechargeable Iodine Batteries: Fundamentals, Advances, and Perspectives

“…For example, during the electrochemical process in the Li–I 2 system, the added NO 3 – could be reduced to NO 2 – accompanied by the formation of active oxygen ions, which would attack the 1,3-dioxolane (DOL) molecules in the electrolyte and induce their polymerization. , The polymerization of DOL, as well as the decomposition of TFSI- anions, led to the formation of solid electrolyte interphase (SEI) layer, which could further prohibit side reactions between lithium anode and iodine species . DFT simulation revealed similar effects of Mg­(NO 3 ) 2 additive in rechargeable Mg–I 2 batteries that the decomposed NO 2 molecules on the Mg metal substrate would prohibit the anode from iodine corrosion by forming a thin protecting layer composed of Mg–N–O …”

“…103 DFT simulation revealed similar effects of Mg(NO 3 ) 2 additive in rechargeable Mg−I 2 batteries that the decomposed NO 2 molecules on the Mg metal substrate would prohibit the anode from iodine corrosion by forming a thin protecting layer composed of Mg−N−O. 104 Despite the fact that the nitrate-containing electrolytes helped restrain the shuttle effect of iodine species, recent research indicated that severe self-discharge behavior would still happen even using a Li anode precycled in a nitrate-containing electrolyte. 95 This result verified that the formed protective layer might not be the only reason for the enhanced electrochemical performance.…”

Metal–iodine batteries: achievements, challenges, and future

“…18f). 249 However, in contrast to Li, when the iodine coverage is increased to 100%, the Mg surface exhibits good resistance to surface iodization without iodide exfoliation. 137 This indicates that the Mg anode could have good resistance to iodization-induced corrosion and self-discharge.…”

Aqueous Rechargeable Zn–Iodine Batteries: Issues, Strategies and Perspectives

“…[21] It has already been confirmed that nitrates like LiNO 3 , NaNO 3, and Mg(NO 3 ) 2 additives performed critical roles in suppressing the shuttling effect and improving Coulombic efficiency. [51] Other additives, such as organic molecules, organic solvents, and nitrates, for improving the performance of Zn//I 2 batteries are worthy to be studied.…”