Intercalation of lithium ions into graphite electrodes studied by AC impedance measurements

Effects of electrolyte concentrations and the level of preintercalation (x values in LixC6) on the lithium ion intercalation into graphite lattices ha ve been examined in propylene carbonate-ethylene carbonate mixed solutions with LiClO4 as an electrolyte by ac impedance measurement techniques. Excha nge current densities were determined for reductive intercalation of lithiu m by ac impedance measurements to range between 1.4 and 2.4 mA/cm(2) depend ing on the amount of intercalated lithium ions with a transfer coefficient (alpha) of 0.65. Diffusion coefficients during the deintercalation process have also been determined at various preintercalation levels. The dependenc e of diffusion coefficients and exchange currents on the x values in LixC6 (x less than or equal to 1) is discussed. (C) 1999 The Electrochemical Soci ety. S0013-4651(98)02-016-5. All rights reserved.