Decomposition temperatures and vapour pressures of selected ionic liquids for electrochemical applications

The thermal behaviour of selected ionic liquids, potentially useful as electrolyte components in electrochemical devices, formed by ammonium or imidazolium cations combined with bis(trifluoromethanesulfonyl)imide (C2F6NO4S2, TFSI) or bis(fluorosulfonyl)imide (F2NO4S2, FSI) anions, was investigated through thermogravimetric analysis (TGA). The liquid with the FSI anion decomposes at lower temperatures than those based on TFSI. Among ionic liquids with the TFSI anion, the stability in scanning mode with different cations decreases in the order 1-ethyl-3-methylimidazolium (C6H11N2, EMI) > N-trimethyl-N-butylammonium (C7H18N, N1114) ≈ N-trimethyl-N(2-methoxyethyl)ammonium (C6H16NO, N111(2O1)) > N,N-diethyl-N-methyl-N(2-methoxyethyl)ammonium (C8H20NO, N122(2O1)) ≈ N-trimethyl-N-propylammonium (C6H16N, N1113). Moreover, the vapour pressure of the six ionic liquids was obtained by means of long-lasting isothermal heating at temperatures between 150 and 300 °C. The highest pressure values were obtained in the order N1114 FSI > EMI TFSI > N122(2O1) TFSI > N1114 TFSI > N111(2O1) TFSI > N1113 TFSI.