As the anode material, natural graphite, polymer-coated natural graphite, carbon-coated natural graphite and artiˆcial graphite were employed. In order to examine the eŠect of solid electrolyte interface (SEI), these samples were exposed to the cycles of charge/discharge. The gas desorption behavior of these samples was investigated by using a technique of thermal desorption spectroscopy. The amount of desorbed gasses signiˆcantly increased after a charge/discharge cycle. The increase of the desorbed amount was associated with gas desorption from SEI formed in theˆrst cycle. The amount of desorbed gasses increases with an irreversible capacity in theˆrst charge/discharge cycle. The irreversible capacity of surface-coated graphite and artiˆcial graphite was lower than that of natural graphite. The surface coating resulted in the decrease of the amount of desorbed gasses and irreversible capacity. The atomic composition was measured by auger electron spectroscopy. Carbon, Oxygen, ‰uorine and phosphorus were observed after a charge/discharge cycle.

It is known that the performance of lithium ion batteries deteriorates as number of cycles increases. In order to investigate the reason for this the deterioration, the surface coverage ofˆlm formation was measured for graphite electrodes with diŠerent stages of number of cycles. Simultaneously, the gas desorption amount was measured. As the number of cycles increased, so did the surface coverage. The gas desorption amount was roughly proportional to the surface coverage. A polymer-coating changes the characteristics of theˆlm, battery performance and gas desorption. These results suggest that deterioration in the battery performance is owing toˆlm formation because theˆlm blocks lithium ion ‰ow at the graphite surface. The expansion of the battery case is owing to gas desorption from the surfaceˆlm. In this study, the reasons for battery performance are claried.