Abstract
The thermal stability of a layered transition metal oxide with complete Al-substitution, Li1-xNi1/3Co1/3Al1/3O2 (NCA1/3), is studied in comparison to its better understood analogue, Li1-xNi1/3Co1/3Mn1/3O2 (NCM), to elucidate information critical to the safety of lithium-ion batteries. NCA1/3 and NCM have crystalline structures with the R-3m space group by high temperature synthesis from coprecipitate precursors. The specific capacities for NCA1/3 and NCM are 115 mAh/g and 180 mAh/g within 2.5-4.5 V. Thermogravimetric analysis coupled with mass spectrometry confirms the loss of oxygen at 271°C and 292°C for NCM and NCA1/3 delithiated to 4.4 V, respectively. The heat generation reaction of delithiated NCM is 91.7 J/g compared to 10.5 J/g for NCA1/3. The improved thermal stability offered by NCA1/3 is attributed to its low Li+ capacity due to the substitution of Al3+ for Mn4+ and its low heat of reaction due to the stability of the intermediate crystalline phases during delithiation and annealing.
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