STM study on graphite/electrolyte interface in lithium-ion batteries: solid electrolyte interface formation in trifluoropropylene carbonate solution

Lithium intercalation within graphite was studied in an electrolyte system, 1 M LiClO4 dissolved in trifluoropropylene carbonate (TFPC). Lithium was intercalated within graphite in TFPC. The reversible capacity obtained (275 mAh g−1) was smaller than that in ethylene carbonate-based solutions while the irreversible capacity was larger (335 mAh g−1). The morphology change of the basal plane of highly oriented pyrolytic graphite (HOPG) was observed by electrochemical scanning tunneling microscopy (STM) to obtain information about passivating film (solid electrolyte interface, SEI) formation in this solvent system. The exfoliation of graphite layers was observed at 1.1 and 1.0 V vs. Li+/Li, and then swelling of graphite layers appeared along step edges at 0.5 V. The feature observed at 0.5 V was considered as SEI itself in this solvent system.