Thermal behavior of electrochemically delithiated Li 1-xNiO 2 (R3̄m or C2/m) up to 400°C was studied by thermogravimetry, differential scanning calorimetry, high temperature X-ray diffraction, and X-ray absorption measurements, and its thermal decomposition mechanism was proposed. Delithiated Li 1-xNiO 2 was thermally decomposed to a spinel phase (Fd3m) at around 220°C. For x ≤ 0.5, Li 1-xNiO 2 was decomposed to LiNiO 2 and LiNi 2O 4 and the fraction of the spinel in the decomposed product increased almost linearly with x. For x > 0.5, Li 1-xNiO 2 was converted into the spinel and this reaction was accompanied by oxygen evolution. On further heating, delithiated Li 1-xNiO 2 of all compositions turned into a rock salt phase (Fm3m) with NiO structure. The temperature for the decomposition of Li 1-xNiO 2 to a spinel was independent of x, however, the temperature for the decomposition to a rock salt phase decreased with increasing x. The thermal behavior of Li 1-xNiO 2 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.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry