The reversible storage capacity of lithium in a mesophase-derived semi-coke, heat-treated (HTT) below 700 degrees C, was found by far exceeding the theoretical value corresponding to the LiC6 composition. A capacity as high as 1660 mAh/g was obtained in the case of carbon, heat-treated at similar to 450 degrees C, when poly(ethylene oxide)-based electrolyte is used in lithium cells operated at 100 degrees C. This great capacity is discussed on the basis of a model where lithium forms multilayers on the external basal surfaces of the nanometric size mesocarbon domains.