Electrochemical lithium storage of sodium titanate nanotubes and nanorods

Layered hydrated sodium titanate nanotubes are synthesized via a hydrothermal reaction in alkaline solution. The as-prepared nanotubes are calcined at different temperatures (300-600 °C) in air. The microstructure of obtained samples is characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It is observed that the calcined products maintain their parent tubular morphologies below 500 °C. After calcinations at 600 °C, the hollow tubular morphology could completely be converted to the short solid nanorod morphology. In the meanwhile, the monoclinic sodium hexatitanate as a main phase is formed in nanorods, coexisted with sodium trititanate as a residual phase. The electrochemical lithium storage of obtained samples is studied by galvanostatic method and cyclic voltammetry. It is demonstrated that the nanotubes calcined at 500 °C have relatively large reversible capacity, good reversibility and excellent high rate discharge capability. The lithium intercalation process is shown to have pseudocapacitive feature caused by their layered structure and open lithium insertion tunnels, which is in favor of the high rate charge/discharge capability of sodium titanate nanotubes.