Porous SnO2 Helical Nanotubes and Sheets for Lithium-Ion Batteries

Motivated by the growing interest in lithium-ion batteries and the good electrochemical performance of Sn-based materials, we report a surfactant-free chemical solution route for synthesizing porous SnO₂ helical nanotubes templated by helical carbon nanotubes and SnO₂ sheets templated by graphite sheets. Transmission electron microscopy, X-ray diffraction, cyclic voltammetry, and galvanostatic discharge-charge analysis are used to characterize the SnO₂ samples. The unique nanostructure and morphology make them promising anode materials for lithium-ion batteries. The discharge capacities in the first and the second cycles are 1252 and 1146 mAh/g for SnO₂ nanotubes, and 1039 and 973 mAh/g for SnO₂ sheets. On the other hand, the charge capacities in the first and the second cycles are 1212 and 1105 mAh/g for SnO₂ nanotubes, 1016 and 950 mAh/g for SnO₂ sheets. The first-cycle irreversible capacity loss is 3.2 % and 2.2 % for the nanotubes and sheets, respectively. The SnO₂ helical nanotubes show a specific capacity of above 800 mAh/g after 10 charge and discharge cycles, exceeding the theoretical capacity of 781 mAh/g for SnO₂. After 30 cycles, the SnO₂ nanotubes still exhibit a discharge capacity of 439 mAh/g and the sheets have a discharge capacity of 323 mAh/g. The capacity of SnO₂ helical nanotubes is higher than that of the SnO₂ nanotubes (less than 300 mAh/g after 30 cycles) prepared by a sol-gel vacuum-suction method using AAO as templates; the SnO₂ nanotubes (240 mAh/g after 20 cycles) prepared by hydrothermal method using Sn nanorods as sacrificial templates; and the SnO₂-carbon nanotubes composite (345 mAh/g). It is also confirmed that the SnO₂ samples with the one-dimensional tubular structure show better electrochemical performance than the two-dimensional sheet structure.