New amorphous oxides as high capacity negative electrodes for lithium batteries:: the LixMVO4 (M = Ni, Co, Cd, Zn; 1<x≤8) series

The crystallized precursors LiMVO4 (M = Co, Ni, Cd, Zn) are irreversibly transformed to lithiated amorphous oxides LixMVO4 (x close to 8) during the first Li insertion in a lithium battery. Under low rate, these amorphous oxides cycle large amounts of Li per formula unit in the 0.02-3 V range (versus Li), with an average voltage in the order of 0.6 V for Li insertion and 1.4 V for Li extraction. In the case of LixNiVO4 at first Li extraction, for example, Delta x = 6.6 and Q = 980 Ah/kg (active material alone) or 900 Ah/kg (calculated with respect to the total mass: material + carbon black) or 4230 Ah/l (active material alone), more than 5.5 times the volumic capacity of graphite. The cycling behavior at fast rate (C/6) was very good with a peculiar increase in capacity with cycle number after an initial decrease. Characterization of lithiated LixNiVO4 samples, performed with the use of local techniques such as X-ray absorption spectra (XAS) and electron energy loss spectroscopy (EELS). led to an evaluation of the average oxidation states of V and Ni and of the electronic transfer from Li to V and Ni. Results are compatible with the crystal chemistry of Ni and V oxides. The Li incorporation/extraction' process in the series LixMVO4 is not a destruction/reconstruction mechanism involving Li2O and M and V metals. However, it seems to be different from a classical topotactic intercalation reaction. (C) 1997 Published by Elsevier Science S.A.