The high energy density of NCM batteries with high nickel content is a key advantage in replacing fossil fuels and promoting clean energy development, at the same time, is also a fundamental cause of serious safety hazards in batteries. Primary and secondary amines can lead to ring-opening polymerization of common ethylene carbonate electrolytes, resulting in an isolation layer between the cathode and the anode, and improving the thermal safety of the battery. In this work, the safety of batteries is considered both at the material level and at the cell level, based on the chemical reactions between amines and the battery components. At the material level, the effect of the presence or absence of amine additives on the thermal stability of the different components of the lithium-ion battery was tested by differential scanning calorimetry. At the cell level, the safety of the whole battery with and without additives was tested by using accelerating rate calorimeter to extract thermal runaway (TR) characteristic temperatures. The addition of the amine resulted in an earlier onset of some of the chemical reactions between the battery components, as well as a significant reduction in total heat release and a decrease in the maximum temperature rise rate, such that TR, was effectively suppressed.

Fluorinated electrolytes possess good antioxidant capacity that provides high compatibility to high-voltage cathode and flame retardance; thus, they are considered as a promising solution for advanced lithium-ion batteries carrying both high-energy density and high safety. Moreover, the fluorinated electrolytes are widely used to form stable electrolyte interphase, due to their chemical reactivity with lithiated graphite or lithium. However, the influence of this reactivity on the thermal safety of batteries is seldom discussed. Herein, we demonstrate that the flame-retardant fluorinated electrolytes help to reduce the flammability, while the lithium-ion batteries with flame-retardant fluorinated electrolytes still undergo thermal runaway and disclose their different thermal runaway pathway from that of battery with conventional electrolyte. The reduction in fluorinated components (e.g., LiPF₆ and fluoroethylene carbonate (FEC)) by fully lithiated graphite accounts for a significant heat release during battery thermal runaway. The 13% of total heat is sufficient to trigger the chain reactions during battery thermal runaway. This study deepens the understanding of the thermal runaway mechanism of lithium-ion batteries employing flame-retardant fluorinated electrolytes, providing guidance on the concept of electrolyte design for safer lithium-ion batteries.