Synthesis and electrochemical evaluation of high capacity nanostructured VO₂ cathodes

A metastable form of vanadium dioxide - designated as VO₂(B) - has been synthesized by an ambient temperature reduction of aqueous vanadate ions with potassium borohydride and sodium dithionite followed by heating in vacuum at 230 °C. The samples have been characterized by X-ray diffraction, thermogravimetric analysis (TGA), infrared spectroscopy, scanning electron microscopy (SEM), and electrochemical discharge-charge cycling in lithium cells. These oxides exhibit a high reversible capacity of>300 mAh/g at 3.5-1 V and a moderate reversible capacity of close to 200 mAh/g at 3.5-2 V with good cyclability in a wide temperature range of -30 to 60 °C. Also, the VO₂(B) cathodes exhibit excellent safety characteristics as indicated by the absence of exothermic peaks below 350 °C in differential scanning calorimetry (DSC).