In-depth investigation of the exothermic reactions between lithiated graphite and electrolyte in lithium-ion battery

Abstract

Thermal runaway is a critical issue for the large application of lithium-ion batteries. Exothermic reactions between lithiated graphite and electrolyte play a crucial role in the thermal runaway of lithium-ion batteries. However, the role of each component in the electrolyte during the exothermic reactions with lithiated graphite has not been fully understood. In this paper, the exothermic reactions between lithiated graphite and electrolyte of lithium-ion battery are investigated through differential scanning calorimetry (DSC) and evolved gas analysis. The lithiated graphite in the presence of electrolyte exhibit three exothermic peaks during DSC test. The reactions between lithiated graphite and LiPF6 and ethylene carbonate are found to be responsible for the first two exothermic peaks, while the third exothermic peak is attributed to the reaction between lithiated graphite and binder. In contrast, diethylene carbonate and ethyl methyl carbonate contribute little to the total heat generation of graphite-electrolyte reactions. The reaction mechanism between lithiated graphite and electrolyte, including the major reaction equations and gas products, are summarized. Finally, DSC tests on samples with various amounts of electrolyte are performed to clarify the quantitative relationship between lithiated graphite and electrolyte during the exothermic reactions. 2.5 mg of lithiated graphite (Li0.8627C6) can fully react with around 7.2 mg electrolyte, releasing a heat generation of 2491 J g−1. The results presented in this study can provide useful guidance for the safety improvement of lithium-ion batteries.