An electrochemical impedance investigation is made on the first lithium intercalation kinetics of mesocarbon microbeads (MCMB) heat-treated at high temperature (2800°C) as the lithium intercalation electrode in a gel electrolyte. The gel electrolyte is synthesized from a mixture containing the reactive monomers in an organic solution. Once the charge of lithium ion proceeds, a solid electrolyte interface (SEI) is formed on the MCMB electrode, and its thickness increases during charging. The growth of SEI resistance is indicated by means of ac impedance measurements. Studies on a MCMB electrode stored in its fully intercalated state showed that part of the extra charge consumed during prolonged storage could be attributed to deintercalation of lithium from the MCMB bulk and its subsequent reaction with electrolyte.