Safety characteristics of Li(Ni0.8Co0.15Al0.05)O2 and Li(Ni1/3CO1/3Mn1/3)O2

Layered Li-0.45(Ni0.8Co0.15Al0.05)O-2 and Li-0.55(Ni1/3Co1/3Mn1/3)O-2 materials have been, respectively, prepared by a chemical delithiation of layered Li(Ni0.8Co0.15Al0.05)O-2 and Li(Ni1/3Co1/3Mn1/3)O-2 compounds using NO2BF4 oxidizer in ail acetonitrile medium. The thermal gravimetric results show that both Li-0.45(Ni0.8Co0.15Al0.05)O-2 and Li-0.55(Ni1/3Co1/3Mn1/3)O-2 powders release oxygen starting from 190 and 250 degrees C with an overall oxygen loss of 11 and 9 wt% at 900 degrees C, respectively. The results show that the oxygen release from these delithiated powders was associated with the occurrence of several structural transformations, ranging from a R (3) over barm -> Fd3m (layered -> spinel) transition to a Fd3m -> Fm3m (spinel -> NiO-type) transition. The 3 wt% weight gain, solely observed for Li-0.55(Ni1/3Co1/3Mn1/3)O-2 between 800 degrees C and room temperature, involved a reversible Fd3m reversible arrow Fm3m (spinel reversible arrow NiO-type) structural transition. The reactivity of these delithiated powders with electrolytes was investigated by a differential scanning calorimetry (DSC) between room temperature and 375 degrees C. In the case of Li-0.55(Ni1/3Co1/3Mn1/3)O-2 powder, the DSC result shows that the oxidation of the electrolyte was delayed by 50 'C toward high temperatures with the generation of lower heat when compared to Li-0.45(Ni0.8Co0.15Al0.05)O-2 powder. The relationship between the safety characteristics of Li-0.45(Ni0.8Co0.15Al0.05)O-2 and Li-0.55(Ni1/3Co1/3Mn1/3)O-2 powders and their thermal stability was discussed in the light of their structural rearrangement during the thermal heating processes. (c) 2005 Elsevier B.V. All rights reserved.