SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF AMORPHOUS VANADATES OF GENERAL FORMULA RVO4 (R = IN, CR, FE, AL, Y) VS. LI

A method is described for the low-temperature preparation of amorphous vanadates of general formula RVO4 (R = In, Cr, Fe, Al, Y), and their electrochemical properties vs. Li are reported. A dissolution-reprecip itation process from a mixed solution of NH4VO3 and R(NO3)(3) was used to prepare these compounds. By appropriate annealing of the amorphous precursors, several crystallized vanadates were obtained as well. Amo ng all of these vanadates, either amorphous or crystallized, only thos e with R = In and Fe are of potential interest as negative electrodes in lithium-ion rechargeable batteries since they display reversible ca pacities as large as 900 mAh/g. This different electrochemical behavio r depending on the nature of the metallic element implies that R is no t just a spectator with respect to the Li uptake into these materials. From both electrochemical and in situ x-ray diffraction data, a mecha nism of Li uptake/removal different from the usual Li insertion/deinse rtion process is proposed.