Physicochemical and electrochemical investigations of the ionic liquid N-butyl -N-methyl-pyrrolidinium 4,5-dicyano-2-(trifluoromethyl)imidazole

• DOI: 10.1016/j.electacta.2017.02.141
• Publication Date: 2017-02-28T00:04:41Z
• Authors: Anders Ochel; Daniele Di Lecce; Christian Wolff; Guk-Tae Kim; Diogo Vieira Carv...; Stefano Passerini
• Keywords: Electrochemical window; Thermal Stability

Abstract A new ionic liquid formed by coupling 4,5-dicyano-2-(trifluoromethyl)imidazole (TDI − ) anion with N- butyl -N- methyl-pyrrolidinium (Pyr 14 + ) cation is successfully synthesized and characterized by Raman spectroscopy, thermal and rheological analyses, as well as electrochemical techniques. The Pyr 14 TDI-LiTDI mixture, melting at 49 °C, shows remarkable stability within the 50–250 °C range, as well as suitable ionic conductivity, lithium ion transport, and electrochemical stability window. Thus, it is proposed for application at 60 °C in a lithium cell with stable LiFePO 4 cathode. At this temperature, the electrolyte has viscosity of 65.8 mPa s, ionic conductivity of the order of 5 mS cm −1 , and limiting current density of 10 −2 mA cm −2 . Lithium metal/LiFePO 4 cells with such an electrolyte offer promising results in terms of stable LiFePO 4 /electrolyte interface, investigated by impedance spectroscopy, as well as delivered capacity above 160 mAh g −1 with 81% of retention after 80 galvanostatic cycles.