Mo-doped Gray Anatase TiO₂: Lattice Expansion for Enhanced Sodium Storage

Gray-colored Mo⁶⁺-doped anatase TiO₂ is prepared uniformly with particle size of 10–20 nm, and is firstly employed as anode material in sodium-ion batteries (SIBs), presenting excellent electrochemical performances. It delivered reversible specific capacities of 231.8 mAh g⁻¹ at 0.1 C (33.5 mA g⁻¹) after 100 cycles and 108.3 mAh g⁻¹ at 5 C (1.68 A g⁻¹), comparing to 170.5 mAh g⁻¹ at 0.1 C and only 41.7 mAh g⁻¹ at 5C for the bare TiO₂. The improved electrochemical performances might be beneficial from the doping of Mo⁶⁺, which can effectively enhance the conductivity of TiO₂ resulting from induced conduction band electrons, interstitial oxygen defects and vacancies. In addition, the doping can also lead to the lattice expansion, which can facilitate the diffusion of Na⁺. In combination with natural abundance and environmental benignity, Mo⁶⁺-doped TiO₂ can be expected to be utilized as an anode material for enhanced sodium storage.