The thermal decomposition reactions of lithium-intercalated graphite electrodes with the electrolyte solution have been investigated by DSC measurements. Three exothermic reaction peaks appeared in the DSC curves around 130°C (peak 1), 260°C (peak 2) and 300°C (peak 3), respectively. The total amount of generated exothermic heat increased linearly with the amount of intercalated lithium, not depending on specific surface area of graphite powder. The increase of specific surface area reduced temperatures of peak 2 and peak 3, and magnified the amount of heat generated at peak 1. The increase of specific surface area is considered to accelerate the thermal decomposition reactions of lithium-intercalated graphite with the electrolyte solution and reaction at peak 1, which was associated with passivation film formation. The reaction around 130°C has been investigated by GC and FT-IR measurements. Li2CO3 was produced on the graphite surface and CO2 gas was evolved during lithium-intercalated graphite heating at 130°C. It was supposed that lithium alkyl carbonate was created on the graphite surface at first and lithium alkyl carbonate was decomposed immediately to Li2CO3, which was more stable.
