SYNTHESIS AND ELECTROCHEMISTRY OF SPINEL LT-LICOO2

A recently reported new phase of LiCoO2, called LT-LiCoO2 (for Low Temperature) by the discoverers, was synthesized at 400-degrees-C by two different methods and examined for use in Li/LiCoO2 cells. The first reports of LT-LiCoO2 give convincing evidence that the compound is layered with the same structure type (space group, R-3M) as LiCoO2 prepared at 850-degrees-C (HT-LiCoO2). HoweVer, LT-LiCoO2 has ideal cubic close packing, and we show here that a better understanding of the diffraction pattern is attained if the structure is assumed to be spinel related with space group Fd3m analogous to Li2Ti2O4. In this structure, the oxygen atoms occupy fully the 32e sites with oxygen positional parameter x=0.257 and Li and Co fully occupy the 16c and 16d octahedral interstices respectively with very little cation mixing. The cubic lattice constant is 7.998(5) angstrom. The electrochemical behaviour of Li/LT-LiCoO2 cells differs greatly from that of HT-LiCoO2 because the former material has the spinel structure and the latter has a layered structure type.