Single walled carbon nanotubes (SWNTs) were reacted with molten lithium at 220 degreesC for two weeks. This induced dramatic changes in their structure as shown by x-ray and electron diffractometry and Raman spectroscopy. A significant fraction of the initial SWNTs transformed into flat nanostrips having intercalated lithium in between them. Lithium forms a superlattice commensurate with that of the graphitelike nanostrips with root 7x root3 in-plane distribution. This new structure corresponds to the LiC10 composition.