Thermal behavior and the decomposition mechanism of electrochemically delithiated Li1-xNiO2

Thermal behavior of Li1-xNiO2 (R (3) over barm or C2/m) up to 400 degreesC was studied using thermogravimetry (TG), differential scanning calorimetry (DSC), and high-temperature X-ray diffraction measurements and its decompos ition mechanism was proposed. Delithiated Li1-xNiO2 was thermally decompose d to LiNi2O4 spinel (Fd3m) at the temperature range of 180-250 degreesC. Fo r x less than or equal to 0.5, Li1-xNiO2 was decomposed to LiNiO2 and LiNi2 O4 and the fraction of the spinel in the decomposed product increased almos t linearly with x. For 0.5 < x less than or equal to 0.8, Li1-xNiO2 was con verted into LiNi2O4 spinel and this reaction was accompanied by oxygen evol ution. Li1-xNiO2 of all compositions turned into a rock-salt phase (Fm3m) w ith oxygen liberation at temperatures above 270 degreesC. The temperature f or the decomposition of Li1-xNiO2 to a spinel or a rock-salt phase decrease d with x in Li1-xNiO2. The thermal behavior of Li1-xNiO2 could be interpret ed as an overlap of the exothermic rearrangement of cations (nickel and lit hium ions) to form a spinel or a rock-salt phase and the endothermic oxygen evolution reaction. (C) 2001 Elsevier Science B.V. All rights reserved.