Thermal stability of NCM811 cathode material for Li-ion batteries

The thermal stability of NCM811 cathode material for lithium (Li)-ion batteries has been studied during annealing using real-time synchrotron x-ray scattering, scanning electron microscopy, and differential thermal analysis (DTA). The DTA and thermogravimetric results revealed that the dehydration of intergranular water within the NCM811 powders occurred between 134 and 150 °C. This phenomenon led to an expansion of the mean particle size, reaching maximum values of 8.9 μm at 200 °C in air and 12.1 μm at 225 °C in vacuum, respectively. Real-time synchrotron x-ray scattering further elucidated the thermal and structural stability of the NCM811 oxide powders during annealing up to 500 °C. The amount of crystal phase was greater in air than in vacuum, while the variation in crystal domain size was less significant in air. These findings indicate that NCM811 powders exhibit enhanced thermal structural stability during annealing in air compared to vacuum, which is attributed to the presence of ambient 21% oxygen.