Coordination–Diffusion Coupling (CDC) in Dual-Anion Ionic-Liquid/Carbonate Electrolytes: Molecular Origins of Lithium-Ion Self-Diffusion
- 1Department of Chemistry
- 2Hawassa University
Abstract
Understanding lithium-ion motion in concentrated ionic-liquid electrolytes requires a description that connects local coordination structure to long-range diffusion. Here we combine dispersioncorrected density functional theory (DFT), natural bond orbital (NBO) analysis, and classical molecular dynamics (MD) simulations to examine [EMI][TFSI]/LiFSI/EC/DMC electrolytes at 298 K. The calculations show that [TFSI]- and [FSI]- possess distinct interaction landscapes: six low-energy [EMI][TFSI] conformers span 0.676–5.170 kJ mol-1 in relative energy and −41.22 to −48.64 kJ mol-1 in interaction energy, whereas the corresponding [EMI][FSI] conformers span 0.163–5.849 kJ mol-1 and −34.62 to −44.19 kJ mol-1, respectively. In the condensed phase, Li+ coordination evolves from predominantly carbonate-mediated solvation in the 0% ionic-liquid system to mixed carbonate/anion coordination at 42.9% ionic-liquid content and exclusively anion coordination in the 100% ionic-liquid system. The Li+ self-diffusion coefficient is nonmonotonic across the reported compositions, decreasing from 28.66 × 10-12 m2 s-1 in the carbonate-rich system to 19.88 × 10-12 m2 s-1 at 42.9% ionic-liquid content and increasing to 27.00 × 10-12 m2 s-1 in the pure ionic-liquid system. FSI- also diffuses faster than TFSI- in the systems for which both are present. These results support a mechanistic picture in which Li+ motion is governed not solely by bulk solvent properties but by the persistence and reorganization of its local coordination environment. Building on this observation, we formulate a Coordination–Diffusion Coupling (CDC) framework that combines Shannon coordination entropy with trajectory-derived coordination exchange kinetics and a complementary timescale ratio between translational displacement and coordination-shell residence. The framework is presented as a physically motivated descriptor for interpreting and ultimately screening electrolyte compositions. Importantly, the present study does not directly calculate electrochemical stability, interfacial decomposition, or a local dielectric constant; those properties are therefore treated as design considerations rather than demonstrated outcomes.
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BibTeX
@misc{wagaye2026coordinationdiffusion,
title = {{Coordination–Diffusion Coupling (CDC) in Dual-Anion Ionic-Liquid/Carbonate Electrolytes: Molecular Origins of Lithium-Ion Self-Diffusion}},
author = {Abraham Molla Wagaye and Abraham molla Wagaye},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15008800/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008800/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Coordination–Diffusion Coupling (CDC) in Dual-Anion Ionic-Liquid/Carbonate Electrolytes: Molecular Origins of Lithium-Ion Self-Diffusion
AU - Abraham Molla Wagaye
AU - Abraham molla Wagaye
PY - 2026
DA - 2026/09/14
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008800/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008800/v1
AB - Understanding lithium-ion motion in concentrated ionic-liquid electrolytes requires a description that connects local coordination structure to long-range diffusion. Here we combine dispersioncorrected density functional theory (DFT), natural bond orbital (NBO) analysis, and classical molecular dynamics (MD) simulations to examine [EMI][TFSI]/LiFSI/EC/DMC electrolytes at 298 K. The calculations show that [TFSI]- and [FSI]- possess distinct interaction landscapes: six low-energy [EMI][TFSI] conformers span 0.676–5.170 kJ mol-1 in relative energy and −41.22 to −48.64 kJ mol-1 in interaction energy, whereas the corresponding [EMI][FSI] conformers span 0.163–5.849 kJ mol-1 and −34.62 to −44.19 kJ mol-1, respectively. In the condensed phase, Li+ coordination evolves from predominantly carbonate-mediated solvation in the 0% ionic-liquid system to mixed carbonate/anion coordination at 42.9% ionic-liquid content and exclusively anion coordination in the 100% ionic-liquid system. The Li+ self-diffusion coefficient is nonmonotonic across the reported compositions, decreasing from 28.66 × 10-12 m2 s-1 in the carbonate-rich system to 19.88 × 10-12 m2 s-1 at 42.9% ionic-liquid content and increasing to 27.00 × 10-12 m2 s-1 in the pure ionic-liquid system. FSI- also diffuses faster than TFSI- in the systems for which both are present. These results support a mechanistic picture in which Li+ motion is governed not solely by bulk solvent properties but by the persistence and reorganization of its local coordination environment. Building on this observation, we formulate a Coordination–Diffusion Coupling (CDC) framework that combines Shannon coordination entropy with trajectory-derived coordination exchange kinetics and a complementary timescale ratio between translational displacement and coordination-shell residence. The framework is presented as a physically motivated descriptor for interpreting and ultimately screening electrolyte compositions. Importantly, the present study does not directly calculate electrochemical stability, interfacial decomposition, or a local dielectric constant; those properties are therefore treated as design considerations rather than demonstrated outcomes.
ER -