Superior Sodium Storage in Na₂Ti₃O₇ Nanotube Arrays through Surface Engineering

Abstract

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 (Na 2 Ti 3 O 7 ) 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 Na 2 Ti 3 O 7 nanotubes, surface deposition of a thin layer of TiO 2 , and subsequent sulfidation. The resulting nanoarrays exhibit a high electrochemical Na‐storage activity that outperforms other Na 2 Ti 3 O 7 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 Na 2 Ti 3 O 7 nanotube anode and Na 2/3 (Ni 1/3 Mn 2/3 )O 2 cathode is capable of delivering a specific energy of ≈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.