Improving the sodiation performance of Na₂Ti₃O₇ through Nb-doping

Highlights: • Na₂Ti₃O₇ rods are fabricated and doped by Nb(V) by a one-step sol-gel method. • The unit cell volume becomes larger and the band gap becomes lower after Nb-doping. • The sodiation performance, especially rate capability, is improved after Nb-doping. - Abstract: Na₂Ti₃O₇ has attracted increasing attention as a promising anode material for Na-ion batteries. However, the low electronic conductivity of Na₂Ti₃O₇ brings about kinetic problems for sodiation. In this study, we report Nb-doped Na₂Ti₃O₇ synthesized from a facile sol-gel method. The obtained Na₂Ti_2.97Nb_0.03O₇ has increased unit cell volume and lowered band gap compared to the pristine Na₂Ti₃O₇. The Na₂Ti_2.97Nb_0.03O₇ shows a high reversible capacity of 189.7 mAh g⁻¹ at 0.2C, a great high-rate performance of 89.4 mAh g⁻¹ at 5C, and great cyclability of 78.5% after 500 cycles. Specifically, the rate capability of Na₂Ti_2.97Nb_0.03O₇ is considerably superior to that of the pristine Na₂Ti₃O₇. The improved sodiation performance suggests Nb-doping is an effective modification for Na₂Ti₃O₇ anode materials.