The intrinsic anodic stability of several anions comprising solvent-free ionic liquids

The advent of lithium-ion or rocking chair rechargeable battery technology has severely stretched the anodic limits of common nonaqueous electrolytes. Salts of the form 1,2-dimethyl-3-propylimidazolium X [where X = AsF{sub 6}{sup {minus}}, PF{sub 6}{sup {minus}}, (CF{sub 3}SO{sub 2}){sub 2}N{sup {minus}}, and (CF{sub 3}SO{sub 2}){sub 3}C{sup {minus}}] were prepared and purified. Linear sweep voltammetry was conducted at 80 C, a temperature at which all four salts were molten, at Pt, W, and glassy carbon working electrodes. The authors found that the intrinsic anodic stability of these anions was in the order (CF{sub 3}SO{sub 2}){sub 3}C{sup {minus}} > (CF{sub 3}SO{sub 2}){sub 2}N{sup {minus}} {approximately} AsF{sub 6}{sup {minus}} > PF{sub 6}{sup {minus}}. These experimental solution-phase oxidation potentials correlated well with gas-phase highest occupied molecular orbital energies calculated by an ab initio technique.