Quantitative studies on the influence of LiPF ₆ on the thermal stability of graphite with electrolyte

To study the mechanism of exothermic reactions of charged graphite in electrolyte with temperature ramping up, the thermal behavior of charged graphite in solvent or electrolytes was investigated by DSC. When the charged graphite was heated up in the EC DMC solvent, the dominant exothermic peak was observed at around 160°C. Both the amount of solvent and the content of intercalated Li had direct effect on the thermal behavior of the peak at around 160°C, indicating that this peak should be caused by the reaction between intercalated Li and solvent. However, when the solvent was replaced with LiPF ₆EC DMC electrolytes, the exothermic peak at around 160°C became mild and the heat values were much smaller, due to SEI formation on the anode. On the other hand, the exothermic heat of the peak at around 160°C decreased significantly with the increase of LiPF ₆ concentration of electrolyte. This phenomenon was discussed by considering the exothermic heat of the reaction between intercalated Li and EC DMC solvent. It is clear that LiPF ₆ is needed in EC DMC to form SEI on the charged graphite.