Controlled synthesis of pure-phase metastable tetragonal Nb2O5 anode material for high-performance lithium batteries

Highlights: • Silicon dioxide coating inhibit the phase change of niobium pentoxide. • Nb-O-Si bond formed between silicon dioxide and niobium pentoxide. • The tetragonal phase niobium pentoxide undergoes a two-phase reaction during lithiation. It's challenging to obtain pure-phase metastable tetragonal niobium pentoxide (M-Nb₂O₅) by conventional heating methods, due to the thermodynamical stable temperature region of M-Nb₂O₅ partially overlaps with that of H- or T-type Nb₂O₅. Herein, the pure-phase M-Nb₂O₅ is synthesized by utilizing the confinement of amorphous SiO₂ shells, and the pure-phase M-Nb₂O₅ (without SiO₂) is investigated as anode material of lithium-ion batteries. The shells can not only cut off the mutual integration among Nb₂O₅ particles, but also inhibit the rearrangement and mobility of the atoms inside via forming Si-O-Nb bond at the interface, thus could widen the thermodynamic and kinetic stability stable regions of the M-Nb₂O₅. The physical and electrochemical performance of pure M-Nb₂O₅ (without SiO₂) is characterized as the anode material of lithium-ion batteries, which exhibits an initial capacity of 246 mAh g^-1, unprecedented high-rate performance (≈86 mAh g^-1 at 4.0Ag^-1) and excellent cycling stability (≈78 mAh g^-1at 2.0Ag^-1 after 1000 cycles).