A Study on the Thermal Behavior of Electrochemically Delithiated Li[sub 1−x]NiO[sub 2]

Thermal behavior of electrochemically delithiated Li 1 − x NiO 2 ( R 3 ¯ m or C 2 / 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 − x NiO 2 was thermally decomposed to a spinel phase ( Fd 3 m ) at around 220°C. For x ⩽ 0.5 , Li 1 − x NiO 2 was decomposed to LiNiO 2 and LiNi 2 O 4 and the fraction of the spinel in the decomposed product increased almost linearly with x . For x > 0.5 , Li 1 − x NiO 2 was converted into the spinel and this reaction was accompanied by oxygen evolution. On further heating, delithiated Li 1 − x NiO 2 of all compositions turned into a rock salt phase ( Fm 3 m ) with NiO structure. The temperature for the decomposition of Li 1 − x NiO 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 − x NiO 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.