Effect of AlF3 Coating on rhermal Behavior of Chemically Delithiated Li-0.35[Ni1/3Co1/3Mn1/3]O-2

Abstract

The thermal behavior of chemically delithiated Li-0.35[Ni1/3Co1/3Mn1/3]O-2 and the AlF3-coated material was studied ill the temperature range from room temperature to 600 degrees C. Thermogravimetric analysis results showed that the uncoated and the AlF3-COated Li-0.35[Ni1/3Co1/3Mn1/3]O-2 powders experienced distinct Weight loss with increasing temperature, Of which the weight loss was ascribed to oxygen release from the active materials. The released oxygen amount was less for the AlF3-coated Li-0.35[Ni1/3Co1/3Mn1/3]O-2 than the uncoated material, probably due to the blocking of the oxygen evolution by the AlF3 coating. The weight loss was associated with the irreversible phase transformation from a rhombohedral layer (R3 (m) over bar) Structure to a cubic spinel (Fd3m) Structure, as confirmed by in situ high-temperature X-ray diffraction. The reduced oxygen release brought about by the AlF3 coating delayed the phase transformation to the Cubic spinel Structure. This entailed shifts of the main exothermic reactions to higher temperatures for the active material in the presence of ail electrolyte. The AlF3 Coating remained oil the Surface of the active material to 300 degrees C. Thereafter, the layer changed to Li-Al-O with increasing temperature, as observed by the time-of-night secondary ion mass spectroscopy. The improved thermal properties of the chemically delithiated AlF3-coated Li-0.35[Ni1/3Co1/3Mn1/3]O-2 were ascribed to the Suppression of oxygen release from the active material, and this, ill turn, retarded the formation of the Cubic spinel phase.