Some new aspects of low-temperature lithium cobalt oxides prepared throughcitric acid precursor route

Low-temperature (LT) lithium cobalt oxides were prepared at 300 degrees C b y the solid-state reaction between Li2CO3 and Co3O4, having various startin g compositions Li1+xCoO2 with x = -0.2, 0.0, 0.2, and 0.4. A finely mixed p recursor of the reacting compounds was obtained in molten citric acid. The morphology observed by scanning electron microscopy (SEM) showed the homoge neous and fluffy nature of the specimens, with a BET specific surface as hi gh as 19 m(2)g(-1). The cubic crystal lattice was found to decrease from a 7.990 to 7.984 Angstrom against Li/Co = 0.62 to 0.90 in molar ratio of the water-leached products. The resistivity and open circuit voltage (OCV) agai nst lithium metal were found to be sensitive to the initial lithium content of the samples. Chemical titration showed that all of the samples containe d an appreciable amount of Co2+ in addition to trivalent cobalt. XANES spec tra supported the presence of tetrahedrally coordinated divalent cobalt. A model is proposed in which oxidation of divalent cobalt explains the electr ochemical charge-discharge irreversibility in the initial cycle. (C) 1999 E lsevier Science Ltd.