Abstract The thermal stability of mixed-solvent electrolytes used in lithium cells was investigated by differential scanning calorimetry (DSC) through the use of airtight containers. The electrolytes used were propylene carbonate (PC) and ethylene carbonate (EC)+PC, in which was dissolved 1 M LiPF 6 , 1 M LiBF 4 , 1 M LiClO 4 , 1 M LiSO 3 CF 3 , 1 M LiN(SO 2 CF 3 ) 2 , or 1.23 M LiN(SO 2 CF 3 )(SO 2 C 4 F 9 ). The influence of lithium metal or the Li 0.5 CoO 2 addition on the thermal behavior of these electrolytes was also investigated. The peak temperature of PC-based electrolytes increased following the order of LiPF 6 4 4 2 CF 3 ) 2 3 CF 3 2 CF 3 )(SO 2 C 4 F 9 ). The order of peak temperature of EC–PC-based electrolytes shows a similar tendency to that of EC–PC-based electrolytes, with the exception of the LiN(SO 2 CF 3 ) 2 electrolyte. The EC–PC-based electrolytes with Li metal show a more stable profile compared with the DSC curves of the PC-based electrolytes with the Li metal. The solid electrolyte interphase (SEI) covers the surface of the Li metal and prevents further reduction of the electrolytes. EC may form a better SEI compared with PC. The PC-based electrolytes of LiSO 3 CF 3 , LiN(SO 2 CF 3 ) 2 and LiN(SO 2 CF 3 )(SO 2 C 4 F 9 ) with the coexistence of Li 0.49 CoO 2 show a broad peak at around 200 °C, which may be caused by the reaction of the Li 0.49 CoO 2 surface and electrolytes. The PC-based electrolytes of LiPF 6 , LiClO 4 and LiBF 4 with Li 0.49 CoO 2 show exothermic peaks at higher temperatures than 230 °C. The peak temperatures of the EC–PC-based electrolytes with the coexistence of Li 0.49 CoO 2 are nearly the same temperature as the EC–PC-based electrolytes.