ASPECTS OF THE LI+ INSERTION INTO LIXMN2O4 FOR 0-LESS-THAN-X-LESS-THAN-1

LiMn2O4 was prepared, from chemical MnO2 and LiNO3, at different temperatures in the range 650-900-degrees-C. It is found that, at the lower temperatures (650-750-degrees-C), LiMn2O4 is different with respect to the one prepared at 900-degrees-C not only in terms of morphology (shape, size and surface area of the particles), but also in terms of characteristics of the cubic unit cell. Indeed, the parameter a for the spinel formed at 750-degrees-C has an initial value of 8.227 angstrom, which decreases in a single phase process to 8.075 angstrom upon electrochemical full delithiation. Conversely, LiMn2O4 synthesized at 900-degrees-C shows a delithiation process occurring, in a first step, in a single phase and, in a second step (x<0.5), in a two-phase process with a1=8.060 angstrom and a2=8.148 angstrom. These differences bring about a much better cycling behaviour for cells using cathodes prepared at the lower temperatures. The importance of the microstructural factor is confirmed by Cr-containing spinels synthesized al 650-750-degrees-C. Their slightly different unit cells also impair their electrochemical performance.