Investigation of Li+ Cation Coordination and Transportation, by Molecular Modeling and NMR Studies, in a LiNTf2-Doped Ionic Liquid-Vinylene Carbonate Mixture

摘要

To increase the safety and stability of lithium-ion batteries, the development of electrolytes based on ionic liquids (ILs) has gained a lot of attention in recent years. However, with graphite electrodes, neat ILs afford weak cycling performance in the absence of organic additives (e.g., vinylene carbonate, VC). The potential formation of a [Li+]-O-VC interaction/coordination could have a major influence on the observed electrochemical behavior of Li-ion batteries. On a specific electrolyte, 1-hexyl-3-methylimidazolium bis-(trifluoromethanesulfonyl)imide [C(1)C(6)Im][NTf2] in association with Li[NTf2] (1 mol L-1) and VC, we performed NOESY, {H-1-Li-7} HOESY correlations, and pulsed field gradient spin-echo NMR measurements, combined with molecular dynamics simulations to determine whether such an interaction/coordination between VC and Li+ ions is noticeable. {Li-7-H-1} HOESY experiment shows the vicinity of VC with [Li+] cation, and strong correlations and association between [Li+] and VC are observed in intense first peaks in radial distribution functions and quantified by the coordination numbers in the first solvation shell between [Li+] and the carbonyl oxygen atom of VC.