Anodic stability of several anions examined by ab initio molecular orbital and density functional theories

The anodic stability of anions is an important factor in determining the maximum operating voltage of lithium-ion cells, if appreciable degradation is to be avoided. A linear correlation was observed between the highest occupied molecular orbital energies calculated by ab initio molecular orbital theory [HF/6-31G(d), 6-31 + G(d,p), 6-311 + G(2d,p)] and the limiting oxidation potentials measured by linear sweep voltammetry, which supports experimental results that inorganic fluorine-containing anions are more resistant against oxidation than their organic counterparts: CF3SO3- < (CF3SO2)(2)N-, (CF3SO2)(3)C-, BF4- < PF6- < AsF6-. The ionization potentials of these anions were also calculated from the energy difference between the anion and the neutral radical by ab initio density functional theory [B3LYP/6-31G(d), 6-31 + G(d,p), 6-311 + G(2d,p)]. This high accuracy procedure explained the subtle energy difference between (CF3SO2)(2)N- and (CF3SO2)(3)C-. (C) 2002 The Electrochemical Society.