Efficient surface modulation of single-crystalline Na(2)Ti(3)O(7) nanotube arrays with Ti(3+) self-doping toward superior sodium storage

Although Na2Ti3O7-based anodes have been widely investigated in sodium-ion batteries (SIBs), their Na+ storage properties especially high-rate capability and long-term cycling durability are far from practical application, because of their intrinsic low conductivity and unsatisfied Na+ diffusion resistance. Here, we report the surface engineering of Na2Ti3O7 nanotube arrays grown in situ on Ti foil through a hydrothermal method and subsequent NH3-assisted calcination. Benefiting from the effective surface modification, the as-derived free-standing electrode possesses highly crystalline surface with favorable Na+ diffusion kinetics and self-incorporation of abundant Ti3+ for improved electronic conductivity. These features enable the electrode to achieve remarkable reversible capacity (237.9 mAh g–1), ultra-high rate capability (88.5 mAh g–1 at 100 C = 17.7 A g–1), and excellent cycling stability (92.32% capacity retention at 50 C after 5000 cycles), which are superior to the counterpart without surface modification, as well as almost all Na2Ti3O7-based anode materials reported so far for SIBs. The outstanding electrochemical performance demonstrates the feasibility of proposed surface modulation in designing more efficient electrode materials for energy storage.Jinlong Liu, Zhenyu Wang, Zhouguang Lu, Lei Zhang, Fangxi Xie, Anthony Vasileff and Shi-Zhang Qia