Anatase TiO2 micro/nano-spheres with rich oxygen vacancies as a high-performance anode material for sodium-ion batteries

In this work, sea urchin-like micro/nano anatase titanium dioxide (TiO2) spheres are fabricated by a facile hydrothermal method and subsequent heat treatment in N2 atmosphere. Benefiting from the unique micro/nano-spheres structure, large specific surface area, and rich oxygen vacancies, this sea urchin-like micro/nano TiO2 spheres exhibit excellent long-cycle stability (204.5 mAh g−1 after 1000 cycles at 1.0 A g−1, with a capacity retention rate of 93.3 %) and superior high-rate performance (137.2 mAh g−1 at 10.0 A g−1). Even at 10.0 A g−1 for 20,000 cycles, it still maintains a reversible specific capacity of 120.5 mAh g−1. CV, EIS and GITT analysis demonstrate that the TiO2 nanospheres exhibit obvious pseudocapacitive behavior, stable reaction kinetics and large Na+ diffusion coefficient during the discharge/charge process. More importantly, the Na-ion full cell assembled with NaVPO4F as a cathode material and TiO2 nanospheres as an anode material also exhibit good cycling stability (142.7 mAh g−1 after 100 cycles at 0.5 A g−1).