Real-time X-ray diffraction measurement of carbon structure during lithium-ion intercalation

A coin-type X-ray diffraction (XRD) cell was constructed using synthetic graphite, ethylene carbonate (EC)-diethyl carbonate (DEC)-based electrolyte and lithium metal. Real-time in situ XRD measurements of Li-ion intercalation into graphite were carried out in order to investigate kinetic phenomena during discharge and charge cycles under conditions similar to those of actual coin-type batteries. Intercalation started at 0.55 V versus Li/Li+. At high doping currents, additional growth of lower stage graphite intercalation compounds (GICs) were observed during open circuit after the cell was discharged to 0 V. In 1 M LIPF6/EC + DEC(1:1), the co-existence region of stage-3 and stage-2 GICs appeared at a very low potential around 0.02 V. Based on these observations, we suggest that an intermediate, which may be reduced solvated lithium ion, is formed on the graphite surface during doping and that the intermediate either intercalates into graphite or reacts with electrolyte solution to form a surface film. (C) 1997 Elsevier Science S.A.