Probing Interactions between Li⁺ and Ether-Functionalized Ionic Liquid Cations Using ¹⁷O and Quantitative ¹H-⁷Li...

Ether-functionalized ionic liquid electrolytes (ILEs) with fluorinated anions enhance Li⁺ mobility through the cation's influence on the Li solvation. Herein, we examine how the cationic oxygen position affects its interactions with Li⁺ at high concentrations of lithium bis(fluorosulfonyl)imide. Advanced nuclear magnetic resonance spectroscopy techniques are employed to probe Li-cation interactions, local oxygen environments, and ion mobilities. In acyclic ether cations, the N-(3-methoxypropyl)-N-methylpyrrolidinium [C_3O1mpyr] exhibits more selective coordination and enhanced Li⁺ diffusivity and transport number relative to 1-methyl-1-(2-methoxyethyl)pyrrolidinium. On the other hand, cyclic ether cations show that Li⁺ remains closest to the ring oxygen, with 3-ethyl-3-methyl-oxazolidinium [C₂moxa] displaying interactions across both the cyclic ether and alkyl chain, whereas 4-ethyl-4-methylmorpholinium presents more localized interactions. Faster Li⁺ transport was observed in [C_3O1mpyr] and [C₂moxa], consistent with stronger Li-cation coordination. These results demonstrate that variations in cation structure can have a strong impact on Li⁺ interactions and ion transport in ILEs.