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

Abstract

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.

High Utilization of Composite Magnesium Metal Anodes Enabled by a Magnesiophilic Coating

“…The binding energy ( E b ) of the Au (111) surface toward a Mg atom is −0.83 eV, much larger than the value of −0.21 eV obtained on the Cu (111) surface (Figure d), suggesting that the Au coating has a better Mg affinity than the Cu substrate. Notably, the interaction between Mg and Au is also stronger than that between Mg and three 1,2-dimethoxyethane (DME) molecules (−0.74 eV, Figure S7), a typical solvated [Mg­(DME) 3 ] 2+ ion pair in conventional ether electrolyte. , From these theoretical results, the magnesiophilicity of Cu foil is seen to be enhanced by the Au coating, which is conducive to regulating the magnesium desolvation/transfer kinetics and deposition behavior.…”

“…Notably, the interaction between Mg and Au is also stronger than that between Mg and three 1,2-dimethoxyethane (DME) molecules (−0.74 eV, Figure S7), a typical solvated [Mg(DME) 3 ] 2+ ion pair in conventional ether electrolyte. 11,15 From these theoretical results, the magnesiophilicity of Cu foil is seen to be enhanced by the Au coating, which is conducive to regulating the magnesium desolvation/transfer kinetics and deposition behavior.…”

“…The ever-increasing applications in smart electronics and electrification call for high-energy-density electrochemical storage systems beyond the capabilities of state-of-the-art lithium-ion batteries (LIBs). − Rechargeable magnesium batteries (RMBs) have attracted academic and industrial attention due to metallic magnesium (Mg) offering a high theoretical volumetric capacity of 3833 mAh cm –3 (vs 2046 mAh cm –3 for metallic lithium and 818 mAh cm –3 for graphite), in addition to its abundant and inexpensive resources. − However, magnesium metal anodes (MMAs) usually exhibit low Coulombic efficiency (CE) and poor cycling stability during Mg plating/stripping cycles in conventional organic electrolytes. − Several effective strategies, such as designing electrolyte formulations, − introducing electrolyte additives, − and constructing artificial solid electrolyte interphases (SEI), − have been conducted to improve the reversibility of MMAs. Despite the exciting progress, most reported MMAs are only cyclable under shallow cycling conditions, − e.g., a typical commercial Mg metal foil (∼0.1 mm thick) with a large theoretical areal capacity of ∼38.33 mAh cm –2 is usually only charged and discharged to a depth of ≤1 mAh cm –2 .…”

A weakly ion pairing electrolyte designed for high voltage magnesium batteries

“…While we observe improved Mg reversibility with TEP, the stability of the Mg anode during long-term cycling is of even greater importance. 12,32,34,35 We investigated Mg||Mg symmetric cell behaviour in different electrolytes. At a practical current density of 2 mA cm −2 and areal capacity of 2 mA h cm −2 (Fig.…”

“…33 Similarly, trimethyl phosphate was utilized to suppress DME decomposition. 34,35 However, TFSI − anion decomposition occurs in the latter, leading to a lifetime of ∼450 hours in symmetric cells at a current density of 0.1 mA cm −2 . 34,35 Nonetheless, the phosphate approach inspired us to design solvents to boost Mg anode stability.…”