Stabilisation of the superoxide anion in bis(fluorosulfonyl)imide (FSI) ionic liquid by small chain length phosphonium cations: Voltammetric, DFT modelling and spectroscopic perspectives

Ionic liquids (ILs) containing the bis(fluorosulfonyl)imide anion, FSI, have been investigated as electrolytes for metal-air batteries. Full chemical reversibility is found reduction of oxygen to superoxide at 60 °C under short time scale conditions cyclic voltammetry a glassy carbon electrode when IL contains small chain length triisobutyl(methyl)phosphonium rather than pyrrolidinium cation. DFT calculations suggest that this consequence higher ion pair association energy and shorter intermolecular distance associated with interaction anion phosphonium Stabilization on longer timescales was also established by spectroscopic techniques based ILs were exposed KO2. Studies stability in related ionic cation fluorosulfonyl(trifluoromethanesulfonyl)imide, FTFSI, or bis(trifluoromethanesulfonyl)imide, TFSI, anions are reported.