Electrochemical degradation of butyltrimethylammonium bis(trifluoromethylsulfonyl)imide for lithium battery applications

Ionic liquids (ILs) are being considered as electrolytes for lithium ion batteries due to their low volatility, high thermal stability, and wide electrochemical windows which are stable at the strongly reducing potentials present in Li/Li⁺ batteries. Lithium metal deposition occurs under strongly reducing conditions and the effect that Li metal and any overpotential has on the stability of ILs is important in furthering the application of ILs in lithium based batteries. Here, N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide was exposed to various potential differences in order to collect and characterize the volatile products. The IL produced more volatile products when exposed to strong reducing potentials which included reactive products such as hydrogen, alkanes, and amines. Water is a known contributor to hydrogen production in reducing environments, but the IL is also a source of hydrogen. If Li⁺ was present, the preferred pathway of reduction was plating of the lithium onto the working electrode, thus decreasing the reaction rate of degraded ILs.