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

Abstract

Well-organized carbon nanotube (CNT)@TiO2 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@TiO2 coaxial nanocables show excellent rate capability and cycling performance compared with both pure CNT and pure TiO2 when used as anode materials for lithium-ion batteries (LIBs). Both the specific capacity in the CNT core and that in the TiO2 sheath are much higher than that of the TiO2-free CNT and that of the CNT-free TiO2 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 TiO2 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 TiO2 because the only very thin protection layer on TiO2 (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.