Construction and destruction of passivating layer on LixC6 in organic electrolytes: an impedance study

The microstructure and thermal stability of the passivating layer formed on LixC6 during electrochemical intercalation reaction is investigated by using electrochemical impedance spectroscopy. A porous structure is inferred from the destruction of the passivating film built in 1 M LiClO4 ethylene carbonate after transferring to 1 M LiClO4/propylene carbonate. The film is shown to be thermally stable, while the electrode suffers from self-discharge. The formation process involves three reactions: gas evolution, film formation and intercalation. In ethylene carbonate-based electrolytes, the resistance of the surface layer is higher in absence of ester co-solvents. The relative importance of the three reactions is used to explain the results.