Cycling ability of γ-butyrolactone-ethylene carbonate based electrolytes

The cycling ability of a carbon electrode in gamma-butyrolactone (BL)-ethylene carbonate (EC) based mixtures has been investigated in the presence of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethylsulfone)imide (LiTFSI), and lithium tetrafluoroborate (LiBF4). LiBF4 is the only salt, which permits full charge-discharge cycles in BL-EC mixtures. The passivation film formed at the carbon electrode has been studied by microscopy and X-ray photoelectron spectroscopy. The cycling ability of the carbon and LixCoO2 electrodes has been evaluated in two BL-EC mixtures (9:1 and 1:1) using LiBF4 (1 M) as an added salt. The wettability of the Celgard separator used in the full-cell configuration has been enhanced by the addition of a surfactant: tetraethylammonium perfluorooctanesulfonate (TEAFOS). This additive does not perturb the quality of the passivative film and increases the wettability by lowering the surface tension of the electrolyte. The electrolyte BL-EC (9:1) + LiBF4 (1 M) has been selected for full-cell cycling experiments at different temperatures (-15 to 25degreesC) in the presence of TEAFOS (0.014 M). (C) 2003 The Electrochemical Society.