SYNTHESIS OF NANOCRYSTALLINE VO2 AND ITS ELECTROCHEMICAL-BEHAVIOR IN LITHIUM BATTERIES

Nanocrystalline VO2 having a metastable shear structure, designated as VO2(B), has been synthesized by a simple chemical method. The procedu re involves a reduction of aqueous potassium vanadate solution with po tassium borohydride around pH 4. The sample has been characterized by x-ray diffraction, differential scanning calorimetry, thermogravimetri c analysis, and transmission electron microscopy. The metastable VO2(B ) begins to transform irreversibly to the more stable monoclinic rutil e VO2 around 350 degrees C and the transformation is complete around 5 00 degrees C. VO2(B) exhibits a maximum reversible capacity of about 3 20 mAh/g in the range 4 to 1 V in lithium cells. A good capacity reten tion on cycling makes it an attractive cathode for rechargeable lithiu m cells. In addition, the excellent cyclability without any capacity d ecline around an intermediate 2.5 V range may become particularly usef ul for the recently suggested aqueous lithium-ion cells consisting of VO2(B) anode and LiMn2O4 cathode.