Symbiotic Coaxial Nanocables: Facile Synthesis and an Efficient and Elegant Morphological Solution to the Lithium Storage Problem

Well-organized carbon nanotube (CNT)@TiO 2 core/porous-sheath coaxial nanocables are synthesized by controlled hydrolysis of tetrabutyl titanate in the presence of CNTs, and investigated with scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and electrochemical experiments. The CNT@TiO 2 coaxial nanocables show excellent rate capability and cycling performance compared with both pure CNT and pure TiO 2 when used as anode materials for lithium-ion batteries (LIBs). Both the specific capacity in the CNT core and that in the TiO 2 sheath are much higher than that of the TiO 2 -free CNT and that of the CNT-free TiO 2 sample, respectively. These results demonstrate that the coaxial cable morphology provides a clever solution to the ionic-electronic wiring problem in LIBs as well as the synergism of the two cable wall materials. On one hand, the CNT core provides sufficient electrons for the storage of Li in TiO 2 sheath. On the other hand, the CNT itself can also store Li whereby this storage kinetics is, in turn, improved by the presence of the nanoporous TiO 2 because the only very thin protection layer on TiO 2 (unlike free CNT) enables rapid access of Li-ions from the liquid electrolyte. This fascinating symbiotic behavior and the fact that the cable morphology leads to an efficient use of this symbiosis makes this solution match the requirements of LIBs extremely well.