Nitrogen Doped/Carbon Tuning Yolk-Like TiO2 and Its Remarkable Impact on Sodium Storage Performances

Yolk-like TiO2 are prepared through an asymmetric Ostwald ripening, which is simultaneously doped by nitrogen and wrapped by carbon from core to shell. It presents a high specific surface area (144.9 m(2) g(-1)), well-defined yolklike structure (600-700 nm), covered with interweaved nanosheets (3-5 nm) and tailored porosity (5-10 nm) configuration. When first utilized as anode material for sodium-ion batteries (SIBs), it delivers a high reversible specific capacity of 242.7 mA h g(-1) at 0.5 C and maintains a considerable capacity of 115.9 mA h g(-1) especially at rate 20 C. Moreover, the reversible capacity can still reach 200.7 mA h g(-1) after 550 cycles with full capacity retention at 1 C. Even cycled at extremely high rate 25 C, the capacity retention of 95.5% after 3000 cycles is acquired. Notably, an ultrahigh initial coulombic efficiency of 59.1% is achieved. The incorporation of nitrogen with narrowing the band gap accompanied with carbon uniformly coating from core to shell make the NC TiO2-Y favor a bulk type conductor, resulting in fast electron transfer, which is beneficial to long-term cycling stability and remarkable rate capability. It is of great significance to improve the energy-storage properties through development of the bulk type conductor as anode materials in SIBs.