The fire and explosion potential risk of Li-ion battery is mainly caused by thermal runaway reactions. A deconvolution method has been proposed to analyze the complex thermal reactions obtained from a reaction, isothermal and scanning calorimeter (C80 microcalorimeter) in this paper. Thermal behaviours of both single electrode system and full cell system under elevated temperature are clearly identified, and separate kinetics is calculated based on the deconvoluted data. According to the analysis, thermal runaway reactions of Li x CoO2/Li x C6 full cell system are comprised by the solid electrolyte interface (SEI) breakdown, melting of separator, short circuit of positive–negative materials, Li x CoO2 disproportionation, lithium (in Li x C6)-electrolyte reaction, further decomposition of Li x CoO2, oxidation of decomposition products of electrolyte and thermal reactions involving polyvinylidene fluoride (PVDF), etc. The thermal stability of SEI, heat generation of positive material and melting temperature of separator are identified as the critical factors that influence the thermal stability of full cell. It is possible to utilize the method for the thermal analysis and the identification of the key factors to thermal control of Li-ion batteries for energy storage and power supply applications.