Protic ionic liquids as electrolytes for high voltage dual ion batteries

Abstract

Protic ionic liquids (PILs) are an interesting class of electrolyte for energy storage devices thanks to their unique properties, which stem from their protonated cations. In this study, we investigate the use of PIL-based electrolyte in dual-ion batteries (DIBs) containing graphite as both positive and negative electrode. Specifically, we considered a mixture of 1-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR_H4TFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Initially, insertion of ${\text{TFSI}}^{-}$ into graphite was investigated, which showed that PIL-based electrolyte allows highly reversible intercalation/de-intercalation processes. Furthermore, kinetics of interfacial charge transfer were analyzed. In the second part of the study, a dual-ion battery containing PIL-based electrolyte was tested. The proof-of-concept graphite-based DIB utilizing this electrolyte delivered a capacity of 54 mAh g⁻¹ at 25 °C while operating in a wide potential window ($\sim$ 5.2 V). The results of these studies demonstrate, for the first time, that the use of PIL-based electrolyte in DIB is possible.