N-doped carbon coated TiO2 hollow spheres as ultralong-cycle-life Na-ion battery anodes

We used a simple solvothermal-pyrolytic two-step route to synthesize N-doped carbon coated anatase TiO2 (TiO2@NC) hollow spheres, where dopamine hydrochloride was simultaneously used as the sources of nitrogen and carbon. The unique hollow structure of the TiO2@NC hollow spheres and the introduced N-doped carbon coating layer resulted in excellent structural stability, facile electrolyte access, high electronic conductivity, short charge-transportation paths, and rapid Na+ reaction kinetics. When applied as Na-ion battery anodes, the TiO2@NC hollow spheres exhibited excellent electrochemical performance, which afforded a high reversible capacity of 260.4 mAh g(-1) at a rate of 0.25C after 300 cycles and was 108.2 mAh g(-1) at 10C even after 10000 cycles, with excellent cycling stability (95.8% retention of the maximum capacity). This superhigh cycling stability is among the highest reported for TiO2/C-based anode materials in Na-ion batteries.