Urea Disrupts Lithium Solvation Shells: Multinuclear NMR and MD Insights into Aqueous Electrolytes Based on Deep Eutectic Solvents
Year: 2026
Type: article
Abstract: The solvation properties of electrolytes are one of the primary drivers of the performance of concentrated aqueous-based batteries. In this study, we provide an understanding of the lithium solvation and its dynamics in an electrolyte derived from a deep eutectic solvent (comprising LiClO 4, urea and water) by effectively correlating multinuclear ( 1 H, 17 O, 35 Cl, and 7 Li) diffusion nuclear magnetic resonance (NMR) spectroscopy with molecular dynamics (MD) simulations. The freely accessible static field gradient from a commercial NMR magnet was used to determine diffusion coefficients for all population-averaged constituents─Li +, ClO 4 –, urea, and water─at various concentrations. The diffusion ratios D Li + / D urea ≈ 1 and D Li + / D ClO 4 – ≈ 1 for the concentrated 1:3:2 electrolyte suggest correlated ionic motion and transport dominated by a vehicular character rather than hopping mechanisms. Ab initio MD simulations reveal mixed Li solvation shell configurations, with substantial urea coordination (∼66% of Li + with one or two urea molecules in the 1:3:2 system) and an increasing occurrence of contact ion pairs with concentration. This results in relatively slow ionic mobility with a cation transference number around 0.5. Ion cluster analysis reveals a systematic increase in the occurrence of contact ion pairs with concentration, yet cluster sizes remain far below percolation thresholds, consistent with vehicular transport. Residence time analysis further quantifies this picture: the characteristic diffusional length exceeds the inner-sphere solvation shell radius ( L c / L s > 1) across all concentrations, providing evidence for vehicular-dominated transport. 17 O diffusion NMR measurements (D 17 O /D 1 H > 1.2 in a concentrated system) provide insights into water dynamics despite significant experimental challenges from quadrupolar relaxation. These findings provide molecular-level insights into aqueous electrolytes based on deep eutectic solvents to further guide the rational design of aqueous battery systems.
Institutions: Centre National de la Recherche Scientifique, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, CEA Paris-Saclay - Etablissement de Saclay, Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Énergie, Queen's University, Queens University, Université Paris-Saclay, Université de Tours, Physico-Chimie des Matériaux et des Électrolytes pour l’Énergie
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7161570906