Structural Characterization of Li1-z-xNi1+zO2 by Neutron Diffraction

Pristine Li1-zNi1+zO2 (z=0.02, 0.07, and 0.25) and deintercalated LixNi1.02O2 (x=0.82 and 0.63) phases were characterized by neutron diffraction. In all cases, the amount of nickel in the lithium sites was found to be identical to that deduced from X-ray diffraction experiments. The sensitivity of the neutron studies allowed us to show that no lithium ions are in the NiO2 slabs for z= 0.02 and 0.07. A Li/Ni mixing appears only for the most lithium-deficient phase leading to the [Li0.73Ni0.27]3b[Ni0.98Li0.02]3aO2 cationic distribution for the Li0.75Ni1.25O2 phase. Determination of the anisotropic atomic displacement parameters confirms the results previously obtained from EXAFS data. The structural characterization of partially deintercalated phases was in good agreement with the XRD analysis. However, in the case of Li0.63Ni1.02O2, it gave evidence for the presence of a small amount of rhombohedral phase due to fluctuations in the composition of the starting material.