Surface analysis of LiMn2O4 electrodes in carbonate-based electrolytes

The interface chemistry of LixMn2O4 electrodes in carbonate-based electrolytes has been investigated using X-ray photoelectron spectroscopy, infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy following cycling or storage in (LiMn2O4 ethylene carbonate/dimethyl carbonate LiPF6/LiBF4\Li] cells. No significant changes were found in the elemental composition of surface films formed on cycled and stored samples, suggesting that surface-film formation is not governed by processes associated with cell cycling. The amount of surface species increases with storage time and cycle number at ambient temperature, where LiF, LixPFyOz products and some polyether-type polymeric compound could be identified as reaction products on the cathode surface. A lithium-rich manganese oxide layer develops on the surface of the cathode particles under continued storage and cycling. The thickness of the surface layer decreases rather than increases with storage at a higher state-of-charge. More carbon compounds are preserved on the electrode surface using LiBF4 rather than LiPF6 as electrolyte salt. (C) 2001 The Electrochemical Society.