Figure 1. Structure and cyclic voltammograms of TEMPO-substituted imidazolium ionic liquids.
Ionic liquids were prepared using modified literature procedures.5-7 Cyclic voltammetry of the ionic liquids in dimethylacetamide with 0.1 M lithium bis(trifluoromethane)sulfonimide was performed using a CHI660D electrochemical workstation in combination with a conventional three-electrode cell. Figure 1 shows cyclic voltammograms for compounds with 4, 5, and 8 carbon atoms in the chains linking the TEMPO and imidazolium moieties. The ionic liquids undergo a reversible electrochemical oxidation reaction at ~0.5 V vs Ag/AgCl (~3.8 V vs Li/Li+) which means that they should be capable of oxidizing the discharge product Li2O2 upon charging to give molecular oxygen and lithium ions. The facilitation of decomposition of Li2O2 can substantially reduce the charge overpotential, thus improving the energy efficiency of Li-O2batteries.
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