COBALT SEGREGATION IN THE LINI1-YCOYO2 SOLID-SOLUTION - A PRELIMINARY LI-7 NMR-STUDY

LiNi1-yCoyO2 materials exhibit a layered structure built from alternate sheets of (Ni,Co)O6 and of LiO6 octahedra sharing edges. They are particularly interesting as positive electrode in rechargeable lithium batteries. Single-pulse Li-7 NMR spectra allow to distinguish between the Li+ ions with only cobalt as their first 3d neighbors and those with at least one Ni3+ (LS t2(6)e1. The small amount of excess Ni2+ ions (t2(6)e2) known to be present in the materials with small y causes an alteration of the spectra. Li+ ions with only cobalt as their first cationic neighbors are detected even for small cobalt contents, which shows the existence of a cobalt segregation while X-rays show that no phase separation occurs.