Raman study of lithium coordination in EMI‐TFSI additive systems as lithium‐ion battery ionic liquid electrolytes

Raman spectroscopy was performed on various mixtures of the ionic liquid salt, 1-ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide (EMI-TFSI). When EMI-TFSI is used in combination with a lithium salt, it could be a potential electrolyte for lithium-ion or lithium metal batteries. The Raman spectra of EMI-TFSI, EMI-TFSI 0.5 M Li-TFSI, EMI-TFSI 0.5 M Li-TFSI 2 M vinylene carbonate (VC) and EMI-TFSI 0.5 Li-TFSI 2 M ethylene carbonate (EC) were collected and compared. A comparison of the peak positions of the δs CF3 mode at 742 cm−1 demonstrates that when carbonate additives are present, the lithium ion is no longer interacting with the TFSI anion. Instead, it is coordinated with the carbon–oxygen double bond of the carbonates. Copyright © 2006 John Wiley & Sons, Ltd.