Seven lithiated and delithiated cathode materials mixed with ethylene carbonate (EC) were studied by differential scanning calorimeter (DSC) for measuring exothermic phenomena. Effects of lithiated and delithiated cathode materials with EC upon the exothermic behaviors were verified and compared. Lithiated cathode materials keep higher stability than delithiated ones. LiCoO2, LiNi0.8Co0.2O2, LiNi1/3Mn1/3Co1/3O2 (NMC333), and LiNi0.5Mn0.3Co0.2O2 (NMC532) react with EC all exhibiting significant exothermic peaks at about (370±20)°C owing to the common component of Co ion. In the delithiated NMC333, NMC532 and LiNi0.8Co0.2O2, effects of Ni ion manifestly resulted in the lower onset temperatures and exothermic peaks than those of lithiated cathode materials. Especially, the onset temperature of delithiated LixNi0.5Mn0.3Co0.2O2 with EC appears at around 98.9°C. EC with delithiated LixCoO2 displaying four peaks has been novel discovered and associated with a strong peak occurred at about 222.2°C. Impacts of Ni, Mn, and Co ions on the thermal stability associated with the structural stability in deliathiated cathode materials under high temperature conditions are discussed.