Thermal stability of the interface between discharged non-graphitizable carbon and electrolyte for lithium-ion batteries

The thermal stability of a non-graphitizable carbon electrode was studied quantitatively by differential scanning calorimetry (DSC). Charged non-graphitizable carbon electrode powder gave exothermic peaks at around 300 °C and the heat values varied depending on the ratio of the electrode powder to coexisting electrolyte solution. Based on the similarities in the exothermic behaviors of charged graphite and non-graphitizable carbon electrodes, the exothermic reactions at around 300 °C should be assigned to the reductive decomposition of a surface film by charged non-graphitizable carbon. On the other hand, non-graphitizable carbon electrode powder showed exothermic reactions at around 290 °C even at a discharged state, while almost no exothermic heat was seen for a discharged graphite electrode powder at temperatures above 250 °C. The heat values decreased as Li-ions in the non-graphitizable carbon electrode were extracted. Based on the present results and a consideration of the slow diffusion and irreversible trapping of Li-ions in non-graphitizable carbon, Li-ions remaining in non-graphitizable carbon could induce exothermic reactions at around 290 °C, even at a discharged state.