MODELING LITHIUM INTERCALATION OF SINGLE-FIBER CARBON MICROELECTRODES

To clarify the electrochemical processes governing the performance of lithiated carbon electrodes and obtain appropriate physicochemical pro perties, experiments conducted with a single-fiber carbon microelectro de (3.5 mu m radius, 1 cm length) are mathematically simulated. Equili brium-potential data are used to determine the activity coefficient of the lithium intercalate and associated host sites. Transport within t he carbon fiber is influenced significantly by activity-coefficient va riations; the use of the guest chemical-potential gradient as the driv ing force for transport phenomena is shown to yield constant physicoch emical properties that are independent of the degree of intercalation. The theoretical calculations display good agreement with several diff erent 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 re action that takes place on the fiber surface.