We describe the first direct in situ measurements of Li transport in an operating cell. Motion of the lithiation front in the graphite electrode suggests that transport could be controlled by liquid-phase diffusion. The electrochemical (current-voltage) data are successfully modeled with a diffusion equation that contains no material or microstructural information. The model is only qualitatively successful in predicting observed Li transport rate data, suggesting that microstructural information is required and that the actual process is more complex than simply diffusion. The technique can provide data for studying Li plating and Li dendrite growth, both of which can cause battery degradation. (C) 2009 Elsevier B.V. All rights reserved.