The capacity fade of Sony 18650S Li-ion cells has been analyzed using cyclic voltammetry, impedance spectroscopy and electron probe microscopic analysis (EPMA). The surface resistance at both the positive (LiCoO2) and negative (carbon) electrodes were found to increase with cycling. This increase in resistance contributes to decreased capacity. Impedance data reveal that the interfacial resistance at LiCoO2 electrode is larger than that at the carbon electrode. The impedance of the positive electrode (LiCoO2) dominates the total cell resistance initially and also after 800 charge–discharge cycles. EPMA analysis on carbon electrodes taken from the fresh and cycled cell show the presence of oxidation products in the case of cycled cells. No change in the electrolyte resistance is seen with cycling.