Thermal Runaway of Lithium-Ion Batteries Employing Flame-Retardant Fluorinated Electrolytes

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.