Kinetic characterization of the electrochemical intercalation of lithium ions into graphite electrodes

Lithium intercalated graphites have taken the place of metallic lithium as anodes for secondary lithium batteries. Controlling the anode-electrolyte interface has been a major technical challenge in the development of lithium-ion battery technologies. The interfacial characteristics can be greatly affected by the kinetics of intercalation. However, the kinetics of the electrochemical intercalation of lithium into graphites has not been well analyzed yet. Very few kinetic and interfacial parameters have been reported. In this work, the electrochemical impedance spectroscopy, constant charge step, and galvanostatic pulse polarization techniques were applied to study the kinetics of the intercalation and deintercalation processes of graphite electrodes in a few important lithium battery electrolyte solutions. Based on the proposed equivalent circuit model, we determined the kinetic and interfacial parameters of the intercalation and deintercalation processes. The measured intercalation charge-transfer resistance, exchange current densities. and intercalation capacitance range between 11 and 28 Omega cm(2), 1.0 and 2.3 mA/cm(2), and 1.0 and 2.0 mu F/cm(2), respectively, depending on the electrolyte solution compositions. The dependence of these kinetic and interfacial parameters on solvent composition, electrolyte concentration, storage time, and intercalated state is discussed. In addition, the transfer coefficients have been determined. The results suggest that the intercalation/deintercalation process is electrochemically reversible. (C) 2000 The Electrochemical Society. S0013-4651(99)11-022-X. All rights reserved.