NEW AMORPHOUS OXIDES AS HIGH-CAPACITY NEGATIVE ELECTRODES FOR LITHIUMBATTERIES - THE LIXMVO4 (M = NI, CO, CD, ZN, 1-LESS-THAN-X-LESS-THAN-OR-EQUAL-TO-8) SERIES

The crystallized precursors LiMVO4 (M = Co, Ni, Cd, Zn) are irreversib ly transformed to lithiated amorphous oxides LixMVO4 (x close to 8) du ring the first Li insertion in a lithium battery. Under low rate, thes e 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 LixNiV O4 at first Li extraction, for example, Delta x = 6.6 and Q = 980 Ah/k g (active material alone) or 900 Ah/kg (calculated with respect to the total mass: material + carbon black) or 4230 Ah/l (active material al one), more than 5.5 times the volumic capacity of graphite. The cyclin g behavior at fast rate (C/6) was very good with a peculiar increase i n capacity with cycle number after an initial decrease. Characterizati on of lithiated LixNiVO4 samples, performed with the use of local tech niques such as X-ray absorption spectra (XAS) and electron energy loss spectroscopy (EELS). led to an evaluation of the average oxidation st ates of V and Ni and of the electronic transfer from Li to V and Ni. R esults are compatible with the crystal chemistry of Ni and V oxides. T he Li incorporation/extraction' process in the series LixMVO4 is not a destruction/reconstruction mechanism involving Li2O and M and V metal s. However, it seems to be different from a classical topotactic inter calation reaction. (C) 1997 Published by Elsevier Science S.A.