Accelerating rate calorimetry studies of the reactions between ionic liquids and charged lithium ion battery electrode materials

Using accelerating rate calorimetry (ARC), the reactivity between six ionic liquids (with and without added LiPF6) and charged electrode materials is compared to the reactivity of standard carbonate-based solvents and electrolytes with the same electrode materials. The charged electrode materials used were Li1Si, Li7Ti4O12 and Li0.45CoO2. The experiments showed that not all ionic liquids are safer than conventional electrolytes/solvents. Of the six ionic liquids tested, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI) shows the worst safety properties, and is much worse than conventional electrolyte. 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI) and 1-propyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide (Py13-FSI) show similar reactivity to carbonate-based electrolyte. The three ionic liquids 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (BMMI-TFSI), 1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide (Pp14-TFSI) and N-trimethyl-N-butylammonium bis(trifluoromethanesulfonyl)imide (TMBA-TFSI) show similar reactivity and are much safer than the conventional carbonate-based electrolyte. A comparison of the reactivity of ionic liquids with common anions and cations shows that ionic liquids with TFSI− are safer than those with FSI−, and liquids with EMI+ are worse than those with BMMI+, Py13+, Pp14+ and TMBA+.