Solvated Li-ion transfer at interface between graphite and electrolyte

Solvated lithium-ion transfer at the interface between the graphite and electrolyte was investigated by ac impedance spectroscopy. Electrolytes consisting of 1 mol dm(-3) LiCF3SO3 dissolved in 1,2-dimethoxyethane (DME) and dimethylsulfoxide (DMSO) were used. Cyclic voltammograms of highly oriented pyrolytic graphite in the above electrolytes showed that solvated lithium ion intercalation occurred below a potential of 1.5 V (vs. Li/Li+). In 1 mol dm(-3) LiCF3SO3/DME electrolyte, impedance spectra of graphite were measured at a potential of 1.1 V. One semicircle was found in the Nyquist plot with a characteristic frequency of 15.8 Hz. For only lithium (nonsolvated lithium) ion intercalation, charge (lithium ion) transfer resistance was observed at a characteristic frequency of less than 0.1 Hz. The temperature-dependence of the charge-transfer resistances for solvated lithium ion transfer and lithium ion-only transfer gave activation energies of around 25 and 53-59 kJ mol(-1), respectively. These results suggest that solvated lithium ion transfer at the interface between graphite and electrolyte should be very fast, and the desolvation process for Li+ ion intercalation and deintercalation at the graphite electrode should play an important role in intercalation/deintercalation kinetics at the interface between electrode and electrolyte. (C) 2004 The Electrochemical Society.