A carbonaceous thin film electrode was prepared by plasma-assisted chemical vapor deposition, and lithium-ion transfer at the interface between the resultant thin film electrode and the electrolyte was studied by AC impedance spectroscopy. On the Nyquist plots, semi-circles assigned as charge (Li+ ion) transfer resistance were observed in the intermediate frequency region. The charge-transfer resistance was dependent on electrode potential. The activation energy for lithium-ion transfer through interface between the electrode and the electrolyte was evaluated, and the value was very large. Hence, it is concluded that a hi h-energy barrier of activation exists at the interface between the electrode and the electrolyte. (C) 2003 Elsevier B.V. All rights reserved.