SYNTHESIS OF LICOO2 FROM COBALT ORGANIC-ACID COMPLEXES AND ITS ELECTRODE BEHAVIOR IN A LITHIUM SECONDARY BATTERY

Well-crystallized, layered LiCoO2 has been prepared by heating cobalt-organic acid complexes (such as malic acid and succinic acid) at 900-degrees-C in air after preheating at 400-degrees-C (2 h) and at 650-degrees-C (6 h). LiCoO2 obtained by this method shows a high (003) peak intensity and low (104) or (101) intensities in X-ray diffraction (XRD). The first discharge capacity of LiCoO2 obtained from this method in ester-based electrolyte is 132 mA h g-1 on cycling between 4.3 and 3.7 V. The value is larger than that obtained by the conventional method. X-ray diffraction studies and open-circuit voltage curves show the presence of at least two types of reaction. A two-phase reaction occurs in the region of 0.71 < x < 1.0 in LixCoO2. The lithiation proceeds as a homogeneous reaction together with expansion of the c-axis in the region of 0.47 < x < 0.71. The expansion of the c-axis against DELTAx change at x = 0.56 corresponds well with the voltage jump observed in the charge/discharge curves.