A study on the thermal behavior of electrochemically delithiated Li1-xNiO2

Thermal behavior of electrochemically delithiated Li1-xNiO2 (R (3) over bar m or C2/m) up to 400 degreesC was studied by thermogravimetry. differential scanning calorimetry, high temperature X-ray diffraction, and X-ray absorp tion measurements, and its thermal decomposition mechanism was proposed. De lithiated Li1-xNiO2 was thermally decomposed to a spinel phase (Fd3m) at ar ound 220 degreesC. For x less than or equal to 0.5, Li1-xNiO2 was decompose d to LiNiO2 and LiNi2O4 and the fraction of the spinel in the decomposed pr oduct increased almost linearly with x. For x > 0.5, Li1-xNiO2 was converte d into the spinel and this reaction was accompanied by oxygen evolution. On further heating, delithiated Li1-xNiO2 of all compositions turned into a r ock salt phase (Fm3m) with NiO structure. The temperature for the decomposi tion of Li1-xNiO2 to a spinel was independent of x, however, the temperatur e for the decomposition to a rock salt phase decreased with increasing x. T he thermal behavior of Li1-xNiO2 could be interpreted as an overlap of the exothermic rearrangement of nickel and lithium cations to form a spinel or a rock salt phase and the endothermic oxygen evolution reaction. (C) 2001 T he Electrochemical Society.