Thermal Stability of Lithium Nickel Oxide Derivatives. Part I: Li<i>_x</i>Ni_1.02O₂ and Li<i>_x</i>Ni_0.89Al_0.16O₂ (<i>x</i> = 0.50 and 0.30)

Abstract

The thermal degradation mechanism of Li x Ni 1.02 O 2 and Li x Ni 0.89 Al 0.16 O 2 ( 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 Al 3+ ions in tetrahedral sites, which disrupts the cationic migrations necessary for the phase transformations observed upon increasing temperature to occur.