The 7 Li NMR T1 relaxation time is shown to be a very severe criterion for determining the stoichiometry of LiCoO 2. When Co 3 O 4 containing minimum impurity level of paramagnetic ions such as Fe or Ni is used as starting material (together with Li 2 CO 3), a T1 value as long as 18 s is obtained but this requires a rather long thermal treatment for complete elimination of excess Li. Such highly stoichiometric Li 1 CoO 2 exhibits a rather early insulator to metal transition upon Li deintercalation. Magnetic susceptibility and specific heat capacity investigations show the exclusive presence of diamagnetic LS Co 3+ .

The influence of the initial Li/Co stoichiometry in LiCoO (LCO) (1.00 ≤ Li/Co ≤ 1.05) on the phase-transition mechanisms occurring at high voltage during lithium deintercalation ( V > 4.5 vs Li/Li) was investigated by in situ X-ray diffraction. Even if the excess Li in LiCoO does not hinder the formation of the H1-3 and O1 phases, the latter are obtained at higher voltages and exhibit larger c parameters compared with their analogues formed from LiCoO. We also showed that for the stoichiometric LiCoO the deintercalation process is more complex than already reported, with the formation of an intermediate structure between H1-3 and O1.

Various P2 and P'3-Na(x)CoO(2) phases, with x ranging approximately from 0.6 to 0.75, have been studied by variable-temperature (23)Na magic angle spinning (MAS) NMR. Signal modification versus temperature plots clearly show that Na(+) ions are not totally mobile at room temperature on the NMR time scale. As the temperature increases, the line shape change of the (23)Na MAS NMR signal differs for the P2 and P'3 stackings and is interpreted by the differences of Na(+) ion sites and of sodium diffusion pathways in the two structures.