Electrochemical investigations of ionic liquids with vinylene carbonate for applications in rechargeable lithium ion batteries

Ionic liquids based on methylpropylpyrrolidinium (MPPY) and methylpropylpiperidinium (MPPI) cations and bis(trifluoromethanesulfonyl)imide (TFSI) anion have been synthesized and characterized by thermal analysis, cyclic voltammetry, impedance spectroscopy as well as galvanostatic charge/discharge tests. 10 wt% of vinylene carbonate (VC) was added to the electrolytes of 0.5 M LiTFSI/MPPY.TFSI and 0.5 M LiTFSI/MPPI.TFSI, which were evaluated in Li parallel to natural graphite (NG) half cells at 25 degrees C and 50 degrees C under different current densities. At 25 degrees C, due to their intrinsic high viscosities, the charge/discharge capacities under the current density of 80 mu A cm(-2) were much lower than those under the current density of 40 mu A cm(-2). At 50 degrees C, with reduced viscosities, the charge/discharge capacities under both current densities were almost indistinguishable, which were also close to the typical values obtained using conventional carbonate electrolytes. In addition, the discharge capacities of the half cells were very stable with cycling, due to the effective formation of solid electrolyte interphase (SEI) on the graphite electrode On the contrary, the charge/discharge capacities of the Li parallel to LiCoO2 cells using both ionic liquid electrolytes under the current density of 40 mu A cm(-2) decreased continually with cycling, which were primarily due to the low oxidative stability of VC on the surface of LiCoO2 Published by Elsevier Ltd.