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 i ntercalated within graphite in TFPC. The reversible capacity obtained (275 mAh g(-1)) was smaller than that in ethylene carbonate-based solutions whil e the irreversible capacity was larger (335 mAh g(-1)). The morphology chan ge of the basal plane of highly oriented pyrolytic graphite (HOPG) was obse rved by electrochemical scanning tunneling microscopy (STM) to obtain infor mation 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 alo ng step edges at 0.5 V. The feature observed at 0.5 V was considered as SEI itself in this solvent system. (C) 1999 Elsevier Science Ltd. All rights r eserved.