Measurements of Chemical Diffusion Coefficient of Lithium Ion in Graphitized Mesocarbon Microbeads Using a Microelectrode

The solid‐state diffusion of lithium ion in carbon was directly investigated in single spherical particles of graphitized mesocarbon microbeads (MCMB, Osaka Gas Co.). In order to achieve electrochemical measurements focusing on a single particle, a molybdenum‐filament microelectrode was maneuvered to make electrical contact with a single MCMB placed in an organic solvent mixture containing lithium ions as an electrolyte. This novel microelectrode technique gives electrochemical information about a MCMB particle, itself, without any dilution with additives such as organic binders. The chemical diffusion coefficient (D) of lithium ion was determined from potential‐step chronoamperograms assuming spherical diffusion of lithium ions in the MCMB particle. The values of D were found to change the order between and depending on the electrode potential. Plots of D showed pronounced minima at the potentials where the transformation of staging level of lithium intercalation compounds occurred. ©1998 The Electrochemical Society