Electrolyte Reactivity on the MgV₂O₄ Cathode Surface.

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Electrode-electrolyte interface instabilities and surface passivation are major challenges in multivalent magnesium batteries.
• Predicting molecular interactions and chemical reactivity of electrolyte components on electrode surfaces is crucial for battery performance.

Purpose of the Study:

• To investigate the intrinsic reactivities of electrolyte species in magnesium bis(trifluoromethanesulfonimide) (Mg(TFSI)2) in diglyme (G2) on a magnesium vanadate (MgV2O4) cathode.
• To elucidate the mechanisms of electrolyte decomposition at the electrode-electrolyte interface.

Main Methods:

• First-principles calculations to study the adsorption and reactivity of electrolyte ions and molecules on MgV2O4.
• Multimodal spectroscopy (X-ray photoelectron, X-ray absorption near-edge structure, electron energy-loss) and transmission electron microscopy.
• Ion soft landing technique to create well-defined electrolyte-MgV2O4 interfaces for experimental analysis.

Main Results:

• Nonsolvated [Mg(TFSI)]+ showed the strongest adsorption on MgV2O4, while partially solvated [Mg(TFSI):G2]+ was the most reactive.
• Predicted C-S bond cleavage in TFSI- and C-O bond cleavage in G2 as dominant decomposition pathways, forming species like CF3- and CH3+.
• Experimental results confirmed electrolyte decomposition and formation of MgF2 and carbonates, particularly with [Mg(TFSI):G2]+, corroborating theoretical predictions.

Conclusions:

• Mg2+ desolvation at the MgV2O4 surface triggers electrolyte decomposition via adsorption and charge transfer, leading to fluoride passivation.
• Surface-induced decomposition is favored over intrinsic gas-phase dissociation.
• Designing anodically stable electrolytes requires systems that facilitate cation desolvation.