Investigation of the N-butyl-N-methyl pyrrolidinium trifluoromethanesulfonyl-N-cyanoamide (PYR14TFSAM) 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 PYR14TFSAM. 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 PYR14TFSAM is not only higher than that of PYR14TFSI, but also higher than that of PYR14FTFSI with 3.8 mS cm−1 at 20 °C and 12.6 mS cm−1 at 60 °C. In addition, the ionic liquid does not crystallize and exhibits a viscosity similar to that of PYR14FSI (and even lower above 30 °C, which also results in a higher conductivity at high temperature). Compared to PYR14DCA, PYR14TFSAM has a higher anodic stability, more compatible with state-of-the-art cathodes such as NCM, even though the PYR14DCA electrolyte also allowed surprisingly good cycling results of NCM cathode considering its low anodic stability. PYR14TFSAM 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.