Control of Carbon Nanotube Electronic Properties by Lithium Cation Intercalation

We show that the electronic properties of single walled carbon nanotubes (SWCNTs) can be tuned continuously from semiconducting to metallic by varying the location of ions inside the tubes. Focusing on the Li(+) cation inside the (26,0) zigzag semiconducting and (15,15) armchair metallic SWCNTs, we found that the Li(+)-SWCNT interaction is attractive. The interaction is stronger for the metallic SWCNT, indicating in particular that metallic tubes can enhance performance of lithium-ion batteries. The electronic properties of the metallic SWCNT are virtually independent of the presence of ions: Li(+) creates an energy level in the valence band slightly below the Fermi energy. On the contrary, the semiconducting SWCNT can be made metallic by placing ions close to the tube axis: Li(+) generates a new bottom of the conduction band. Letting the ions approach SWCNT walls recovers the semiconducting behavior.