Safety characteristics of Li(Ni_0.8Co_0.15Al _0.05)O₂ and Li(Ni_1/3Co_1/3Mn _1/3)O₂

Layered Li_0.45(Ni_0.8Co_0.15Al _0.05)O₂ and Li_0.55(Ni_1/3Co _1/3Mn_1/3)O₂ materials have been, respectively, prepared by a chemical delithiation of layered Li(Ni_0.8Co _0.15Al_0.05)O₂ and Li(Ni_1/3Co _1/3Mn_1/3)O₂ compounds using NO ₂BF₄ oxidizer in an acetonitrile medium. The thermal gravimetric results show that both Li_0.45(Ni_0.8Co _0.15Al_0.05)O₂ and Li_0.55(Ni _1/3Co_1/3Mn_1/3)O₂ powders release oxygen starting from 190 and 250°C with an overall oxygen loss of 11 and 9 wt% at 900°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 R3̄m→Fd3m (layered → spinel) transition to a Fd3m → Fm3m (spinel → NiO-type) transition. The 3 wt% weight gain, solely observed for Li_0.55(Ni _1/3Co_1/3Mn_1/3)O₂ between 800°C and room temperature, involved a reversible Fd3m←Fm3m(spinel←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°C. In the case of Li_0.55(Ni _1/3Co_1/3Mn_1/3)O₂ 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(Ni_0.8Co_0.15Al_0.05)O ₂ powder. The relationship between the safety characteristics of Li_0.45(Ni_0.8Co_0.15Al_0.05)O ₂ and Li_0.55(Ni_1/3Co_1/3Mn _1/3)O₂ powders and their thermal stability was discussed in the light of their structural rearrangement during the thermal heating processes.