Ultrathin Ti2 Nb2 O9 Nanosheets with Pseudocapacitive Properties as Superior Anode for Sodium-Ion Batteries.

Sodium-ion batteries are emerging as promising candidates for grid energy storage because of the abundant sodium resources and low cost. However, the identification and development of suitable anode materials is far from being satisfactory. Here, it is demonstrated that the Ti2 Nb2 O9 nanosheets with tunnel structure can be used as suitable anode materials for sodium-ion batteries. Ti2 Nb2 O9 nanosheets are synthesized by liquid exfoliation combined with topotactic dehydration, delivering a high reversible capacity of 250 mAh g-1 at 50 mA g-1 at a suitable average voltage of ≈0.7 V. It is found that a low energy diffusion barrier, enlarged interlayer spacing, and exceptional nanoporosity together give rise to high rate performance characterized by pseudocapacitive behavior. The observed high reversible capacity, excellent rate capability, and good cyclability of Ti2 Nb2 O9 nanosheets make this material competitive when compared to other sodium insertion anode materials.