Electrochimica Acta, Vol.250, 25-34, 2017
Investigation of the N-butyl-N-methyl pyrrolidinium trifluoromethanesulfonyl-N-cyanoamide (PYR(14)TFSAM) ionic liquid as electrolyte for Li-ion battery
A new asymmetrical anion, trifluoromethanesulfonyl-N-cyanoamide (TFSAM(-)), was paired with N-butyl- N-methyl pyrrolidinium (PYR14+) to prepare PYR(14)TFSAM. It has been investigated for Li-ion battery application and compared to its PYR14+ analogs paired with either the dicyanamide anion (DCA) or other anions (i.e. bis(trifluoromethanesulfonyl) imide (TFSI-), bis(fluorosulfonly) imide (FSI-), trifluoromethanesulfonyl-fluorosulfonyl imide (FTFSI-)). The conductivity of PYR(14)TFSAM is not only higher than that of PYR14TFSI, but also higher than that of PYR14FTFSI with 3.8 mS cm(-1) at 20 degrees C and 12.6 mS cm(-1) at 60 degrees C. In addition, the ionic liquid does not crystallize and exhibits a viscosity similar to that of PYR14FSI (and even lower above 30 degrees C, which also results in a higher conductivity at high temperature). Compared to PYR(14)DCA, PYR(14)TFSAM has a higher anodic stability, more compatible with state-of-the-art cathodes such as NCM, even though the PYR(14)DCA electrolyte also allowed surprisingly good cycling results of NCM cathode considering its low anodic stability. PYR(14)TFSAM also allows Li+ (de-)/insertion into graphite, using vinylene carbonate as additive. When used in conventional Li-ion electrolyte solvents, it leads to moderate conductivity (as compared with LiFSI or LiTFSI), although much higher than LiDCA. Additionally, it is shown that, even in EC/DMC-based electrolyte, LiTFSAM does not induce Al corrosion at 4.2 V. (C) 2017 Elsevier Ltd. All rights reserved.