Superior Sodium Storage in Na2Ti3O7 Nanotube Arrays through Surface Engineering

Sodium-ion batteries have attracted extraordinary attention owing to their low cost and raw materials in abundance. A major challenge of practical implementation is the lack of accessible and affordable anodes that can reversibly store a substantial amount of Na ions in a fast and stable manner. It is reported that surface engineered sodium titanate (Na2Ti3O7) nanotube arrays directly grown on Ti substrates can serve as efficient anodes to meet those stringent requirements. The fabrication of the nanotube arrays involves hydrothermal growing of Na2Ti3O7 nanotubes, surface deposition of a thin layer of TiO2, and subsequent sulfidation. The resulting nanoarrays exhibit a high electrochemical Na-storage activity that outperforms other Na2Ti3O7 based materials. They deliver high reversible capacities of 221 mAh g(-1) and exhibit a superior cycling efficiency and rate capability, retaining 78 mAh g(-1) at 10 C (1770 mA g(-1)) over 10 000 continuous cycles. In addition, the full cell consisting of Na2Ti3O7 nanotube anode and Na-2/3(Ni1/3Mn2/3)O-2 cathode is capable of delivering a specific energy of approximate to 110 Wh kg(-1) (based on the mass of both electrodes). The surface engineering can provide useful tools in the development of high performance anode materials with robust power and cyclability.