The reactivity between charged positive electrodes of (NMC) and traditional carbonate-based electrolyte (1.09 mol/kg LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7 by weight)) with or without different electrolyte additives at elevated temperatures was methodically investigated using accelerating rate calorimetry (ARC). NMC samples studied included single crystal Li1-n[Ni0.5Mn0.3Co0.2]O2 (SC-NMC532), Al2O3-coated Li1-n[Ni0.6Mn0.2Co0.2]O2 (NMC622A) and Li1-n[Ni0.6Mn0.2Co0.2]O2 coated with a proprietary high voltage coating material (NMC622B). The results from this work are compared to previous studies of other NMC materials made using the same methods to build a “library” of comparative results. The ARC results illustrate that the upper cut-off potential and sample morphology, influence the thermal stability of NMC materials, while additives and coatings have a smaller effect. Some outcomes of the work are that the single crystal morphology of NMC532 appears to lead to enhanced thermal stability compared to traditional NMC532 morphology and that NMC811 is significantly more reactive than all the other grades.