A new method for the determination of apparent diffusion coefficients of lithium ions in graphite electrodes was developed. In situ colorimetry - a technique relating the color of an electrode to its state of charge - was used to measure the distribution of lithium ions in model battery electrodes with good local and temporal resolution. Diffusion kinetics data are obtained from the rate of equilibration of a deliberately induced heterogeneous lithium distribution. An apparent activation energy of ca. 17 kJ/mol was measured for the diffusion of lithium in a porous graphite electrode. (C) 2009 Elsevier B.V. All rights reserved.