A synergetic promotion of sodium-ion storage in titania nanosheets by superlattice assembly with reduced graphene oxide and Fe-doping strategy

Titania has been taken as one promising anode material for sodium ion batteries because of its long cycling stability and suitable working voltage. One of the main bottlenecks for its use is the low capacity. To overcome this challenge, in this work, restacked two dimensional (2D) titania nanosheets, which has an open edge and enlarged interlayer spacing for the ion diffusion, have been doped with Fe elements and hetem-assembled with the conductive reduced graphene oxide (rGO). The conductive rGO added increased the charge transfer at the interface of anode and electrolyte, decreased the diffusion barrier of Na+ inside the composites and increased the stability of titania nanosheet during the charge and discharge process, increasing the capacity and long cycle stability of the anode. The high concentration doping of Fe in the titania nanosheets further decreased the Na+ diffusion barrier, increased the electrical conductivity of the composites and greatly increased the storage sites of Na+. The as obtained superlattice composites of Ti0.67Fe0.3O2/rGO showed a sodium ion capacity of 378.8 mA h g(-1) at 0.1 A g(-1) after 100 cycles, which is the highest values among all reported Ti and Fe oxide materials. It still delivered a stable capacity of 287.4 mA h g(-1 )at high current charge density (1 A g(-1)) after a long cycling process (3000 cycles).

Automated summary

Doped restacked 2D titania nanosheets with Fe elements and assembled with conductive rGO can enhance charge transfer, decrease Na+ diffusion barrier, increase stability of titania nanosheet, leading to improved capacity and long cycle stability of anode. The superlattice composites of Ti0.67Fe0.3O2/rGO exhibited high sodium ion capacity and stable performance even after long cycling process.