Enhancing Lithium and Sodium Storage Properties of TiO₂(B) Nanobelts by Doping with Nickel and Zinc

Nickel- and zinc-doped TiO₂(B) nanobelts were synthesized using a hydrothermal technique. It was found that the incorporation of 5 at.% Ni into bronze TiO₂ expanded the unit cell by 4%. Furthermore, Ni dopant induced the 3d energy levels within TiO₂(B) band structure and oxygen defects, narrowing the band gap from 3.28 eV (undoped) to 2.70 eV. Oppositely, Zn entered restrictedly into TiO₂(B), but nonetheless, improves its electronic properties (E_g is narrowed to 3.21 eV). The conductivity of nickel- (2.24 × 10^-8 S·cm^-1) and zinc-containing (3.29 × 10^-9 S·cm^-1) TiO₂(B) exceeds that of unmodified TiO₂(B) (1.05 × 10^-10 S·cm^-1). When tested for electrochemical storage, nickel-doped mesoporous TiO₂(B) nanobelts exhibited improved electrochemical performance. For lithium batteries, a reversible capacity of 173 mAh·g^-1 was reached after 100 cycles at the current load of 50 mA·g^-1, whereas, for unmodified and Zn-doped samples, around 140 and 151 mAh·g^-1 was obtained. Moreover, Ni doping enhanced the rate capability of TiO₂(B) nanobelts (104 mAh·g^-1 at a current density of 1.8 A·g^-1). In terms of sodium storage, nickel-doped TiO₂(B) nanobelts exhibited improved cycling with a stabilized reversible capacity of 97 mAh·g^-1 over 50 cycles at the current load of 35 mA·g^-1.