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 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. In 1 mol 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 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 ion intercalation and deintercalation at the graphite electrode should play an important role in intercalation/deintercalation kinetics at the interface between electrode and electrolyte. © 2004 The Electrochemical Society. All rights reserved.