Modeling lithium intercalation of single-fiber carbon microelectrodes

To clarify the electrochemical processes governing the performance of lithiated carbon electrodes and obtain appropriate physicochemical properties, experiments conducted with a single-fiber carbon microelectrode (3.5 mu m radius, 1 cm length) are mathematically simulated. Equilibrium-potential data are used to determine the activity coefficient of the lithium intercalate and associated host sites. Transport within the carbon fiber is influenced significantly by activity-coefficient variations; the use of the guest chemical-potential gradient as the driving force for transport phenomena is shown to yield constant physicochemical properties that are independent of the degree of intercalation. The theoretical calculations display good agreement with several different experimental data sets. The diffusion coefficient of lithium in partially graphitic carbon is obtained along with rate constants (i.e., the exchange current density) associated with the electrochemical reaction that takes place on the fiber surface.