γ-Na_0.96V₂O₅: 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 γ-Na_0.96V₂O₅, is easily synthesized by chemical sodiation of the γ′-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 γ-Na_0.96V₂O₅ 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 γ-LiV₂O₅ 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/5. The structural reversibility of the sodium extraction-insertion reaction in γ-Na_0.96V₂O₅ is demonstrated upon cycling. This new vanadium bronze competes with the well-known cathode materials for sodium-ion batteries such as NaNi_1/3Mn_1/3Co_1/3O₂ and NaFePO₄.