Lithium fully inserted into both graphitizable and non-graphitizable carbons has been investigated by Li-7-NMR spectroscopy at low temperatures. It was found that lithium only in the non-graphitizable carbons heat-treated at ca. 1000 degrees C showed peak separation phenomena at temperatures below - 30 degrees C. This peak separation is explained as exchange of lithium nuclei between different kinds of lithium species in the carbons. In addition, an equilibrium relationship between the lithium species in the non-graphitizable carbons was found in the temperature range from -30 to - 150 degrees C.