γ-Na0.96V2O5: A New Competitive Cathode Material for Sodium-Ion Batteries Synthesized by a Soft Chemistry Route

A new cathode material for sodium-ion batteries, the sodium vanadium bronze gamma-Na0.96V2O5, is easily synthesized by chemical sodiation of the gamma'-V2O5 polymorph at room temperature. This low-cost soft chemistry route leads to fine particles with high purity and high crystallinity. The crystal features and morphology of the gamma-Na0.96V2O5 material have been characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. It exhibits a layered structure with orthorhombic symmetry (Pnma space group) isomorphic to that of the lithiated gamma-LiV2PO5 bronze. This cathode material is evaluated by charge discharge experiments. Promising electrochemical performance is outlined. A quantitative Na extraction process is observed at a high voltage of 3.4 V versus Na+/Na, and a reversible electrochemical behavior is demonstrated with an initial specific capacity of 125 mAh g(-1), which remains at 112 mAh g(-1) after 50 cycles at C/S. The structural reversibility of the sodium extraction insertion reaction in gamma-Na0.96V2O5 is demonstrated upon cycling. This new vanadium bronze competes with the well-known cathode materials for sodium-ion batteries such as NaNi1/3Mn1/3Co1/3O2 and NaFePO4.