Thermal stability of lithium nickel oxide derivatives. Part I: LixNi1.02O2 and LixNi0.89Al0.16O2 (x = 0.50 and 0.30)

The thermal degradation mechanism of LixNi1.02O2 and LixNi0.89Al0.16O2 (x = 0.50 and 0.30) was studied by in situ X-ray diffraction correlated with thermal gravimetric analysis coupled with mass spectrometry. The degradation mechanism appears to be the same for both types of samples. It consists of two steps:  the first step, corresponding to the lamellar to pseudo-spinel transformation, is accompanied by an oxygen loss only for compounds with an initial (Li + M)/O ratio (M = Ni, Al) smaller than 3/4. The second step corresponds to the progressive transformation to a NiO-type structure, with an oxygen loss for both initial lithium compositions. The thermal stabilization obtained by partial aluminum substitution for nickel can be explained by the stability of the Al3+ ions in tetrahedral sites, which disrupts the cationic migrations necessary for the phase transformations observed upon increasing temperature to occur.