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.

Solvent Molecule Design Enables Excellent Charge Transfer Kinetics for a Magnesium Metal Anode

“…Although it may still undergo subsequent desolvation reaction and be reduced to metallic Mg, the higher reduction overpotential (significantly higher Δ G ‡ 1 ) and weakened C–O bond indicate that the DME molecule is more likely to decompose through a C–O bond breaking reaction. The situation is consistent with the results of Filhol’s group and Yang’s group that the Mg deposition reaction could compete with electrolyte decomposition in the Mg­(TFSI) 2 /DME electrolyte, leading to decomposition products within the deposition layer. ,, From overall situation, the apparent activation free energy (Δ G ‡) of the Mg electrodeposition process depends on the larger one between Δ G ‡ 1 and Δ G ‡ 2 . And ranked from largest to smallest, the order of Δ G ‡ in four electrolytes is DME (71.4 kJ/mol), S3 (38.4 kJ/mol), S1 (16.3 kJ/mol), and S2 (6.2 kJ/mol), which is greatly consistent with the overpotentials in Mg//Mg symmetric cells (The detailed values of Δ G ‡ 1 and Δ G ‡ 2 for four solvents are shown in Table S2).…”

“…This remarkable work is a milestone in RMBs and shows the feasibility of promoting interfacial kinetics to achieve high-performance Mg batteries. Besides, Yang and co-workers proposed the trimethyl phosphate (TMP) molecule to compete with 1,2-dimethoxyethane (DME) and replace one of the three bound DME molecules for the coordination with Mg 2+ because of the electron-rich phosphorus–oxygen bond . This rearranged solvation sheath can soften the structure deformation of bound DME, leading to a low polarization and a superior cycling performance.…”

“…Besides, Yang and co-workers proposed the trimethyl phosphate (TMP) molecule to compete with 1,2-dimethoxyethane (DME) and replace one of the three bound DME molecules for the coordination with Mg 2+ because of the electron-rich phosphorus−oxygen bond. 52 This rearranged solvation sheath can soften the structure deformation of bound DME, leading to a low polarization and a superior cycling performance. However, the relationship between solvated structures and interfacial kinetics processes still lacks an in-depth investigation, and universal design rules of additive or solvent molecules are not revealed.…”

Rapidly Deformable Vitrimer Epoxy System with Supreme Stress‐Relaxation Capabilities via Coordination of Solvate Ionic Liquids

“…Using these combinations, we also aimed to maximize the stress‐relaxation performance of a vinylogous urethane‐based epoxy vitrimer. To the best of our knowledge, there have been few reports on magnesium and zinc‐based SILs, [ 17 ] and this is the first report on the application of SILs to a vitrimer system. The objectives of using the SILs were as follows: 1) Elimination of metal‐salt mixing processes that may induce unwanted pre‐gelation or compromise mechanical strengths, 2) Enhancement of the catalytic activity of the metal cations during epoxy curing, and 3) Acceleration of the dynamic exchange reaction in cured vitrimer epoxy with a minimum catalyst dose ( Figure ).…”

In Situ Formed Magnesiophilic Sites Guiding Uniform Deposition for Stable Magnesium Metal Anodes

“…Although lithium-ion batteries (LIBs) have prevailed as the dominant technology for energy storage, rising energy demands arising from impending climate change and soaring global population have prompted the search for alternative battery technologies with higher energy densities, enhanced safety, and lower costs. − Moreover, given the relative scarcity of lithium resources, phasing out lithium for more abundant elements has also garnered increasing attention in recent years. , Among various post-LIBs technologies, rechargeable magnesium batteries (RMBs) stand out owing to magnesium’s (Mg) relative high abundance and high theoretical volumetric capacity of 3833 mAh cm –3 . , Nevertheless, a myriad of problems still plague Mg anodes and hinder their practical adoption, including surface passivation and nonuniform Mg deposition. − …”