(684e) Performance of Ternary Ionic Liquid–Lithium Salt Mixtures for Li-O2 Batteries

Identification of stable electrolyte materials which can operate in an oxygen rich atmosphere is a major challenge for the development of the Li-O₂ battery. Conceivably, a hydrophobic room temperature ionic liquid (IL) electrolyte, because of its low volatility, can prevent the hydrolysis reaction at the Li anode and drying of the O₂ electrode during cycling. Pyrrolidinium IL can create a passivation layer on the Li anode and is stable against highly reactive superoxide O₂^-. However, it has a high viscosity and low O₂ solubility that is detrimental to cell performance. Ternary IL mixtures comprised of both high ionically conductive and less viscous imidazolium (i.e., 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl imide (BMIMTFSI)) and pyrrolidinium (i.e., N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR₁₄TFSI)) based ILs are tested as the electrolyte for Li-O₂ batteries. 4:1 (80/20 v/v%)  BMIMTFSI : PYR₁₄TFSI based ternary mixtures show excellent cyclability with 330 mAhg^-1 over 50 cycles at a current density of 0.1 mA.cm^-2, much better than the pure BMIMTFSI, PYR₁₄TFSI and TEGDME electrolytes. The results clearly show the beneficial synergic effect of the two ionic liquids on the electrochemical properties of the mixtures.