Ab Initio Structures and Vibrational Spectra of Li[C(CF3SO2)3] and Li[CH(CF3SO2)2]

The structures and vibrational spectra for the anions [C(CF 3 SO 2 ) 3 ] - and [CH(CF 3 SO 2 ) 2 ] - as well as their ion pairs with lithium have been calculated. Ab initio self-consistent field molecular orbital Hartree−Fock and density functional theory calculations, using the hybrid B3LYP functional, have been performed, both using the 6-31G* basis set. The results are compared with earlier calculational work on the more commonly used TFSI anion, [N(CF 3 SO 2 ) 2 ] -, and with experimental IR spectra. The localization of the single negative charge toward the SO 2 groups is slightly less pronounced in the [C(CF 3 SO 2 ) 3 ] - anion, which results in a lower lithium ion affinity. Also, the double bond character for the central S x − C1 bonds is smaller compared to that of [CH(CF 3 SO 2 ) 2 ] - . The two anions' advantages/disadvantages as polymer electrolyte components are discussed.