Synthesis and electrochemical properties of high capacity V₂O_5-δ cathodes

Metastable vanadium oxides V₂O_5-δ with 0.02 ≤ δ ≤ 0.23 have been synthesized by decomposing ammonium metavanadate under vacuum at 280-350°C. The samples have been characterized by X-ray diffraction, infrared spectroscopy, wet-chemical analyses, and scanning electron microscopy. An evaluation of the V₂O_5-δ oxides in lithium cells reveals that these oxides exhibit high capacities of over 300 mAh/g at 3.8-1.5 V. Although the total capacity occurs over a wide voltage range, moderate capacities of around 200 mAh/g could be readily realized in a narrow practical voltage window of 3.8-2.4 V. The V₂O_5-δ cathodes exhibit good cyclability over a wide range of temperatures (-30 to 60°C) with excellent safety characteristics as indicated by differential scanning calorimetry.