Tailoring Coordination in Conventional Ether-Based Electrolytes for Reversible Magnesium-Metal Anodes

Rechargeable magnesium (Mg) batteries based on conventional electrolytes are seriously plagued by the formation of the ion-blocking passivation layer on the Mg metal anode. By tracking the Mg2+ solvation sheath, this work links the passivation components to the Mg2+-solvents (1,2-dimethoxyethane, DME) coordination and the consequent thermodynamically unstable DME molecules. On this basis, we propose a methodology to tailor solvation coordination by introducing the additive solvent with extreme electron richness. Oxygen atoms in phosphorus-oxygen groups compete with that in carbon-oxygen groups of DME for the coordination with Mg2+, thus softening the solvation sheath deformation. Meanwhile, the organophosphorus molecules in the rearranged solvation sheath decompose on the Mg surface, increasing the Mg2+ transport and electrical resistance by three and one orders of magnitude, respectively. Consequently, the symmetric cells exhibit superior cycling performance of over 600 cycles with low polarization.

Automated summary

By tracking the Mg2+ solvation sheath, this study identifies the components that lead to the formation of the passivation layer and proposes a method to modify the solvation coordination. By introducing an additive solvent with extreme electron richness, the solvation sheath is softened, resulting in improved Mg2+ transport and reduced electrical resistance on the Mg metal anode. This leads to excellent cycling performance.