Passivating Lithiated Graphite via Targeted Repair of SEI to Inhibit Exothermic Reactions in Early-Stage of Thermal Runaway for Safer Lithium-Ion Batteries

The self-exothermic in early stage of thermal runaway (TR) is blasting-fuse for Li-ion battery safety issues. The exothermic reaction between lithiated graphite (LiC_x) and electrolyte accounts for onset of this behavior. However, preventing the deleterious reaction still encounters hurdles. Here, we manage to inhibit this reaction by passivating LiC_x in real time via targeted repair of SEI. It is shown that 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (D₃F) can be triggered by LiC_x to undergo ring-opening polymerization at elevated temperature, so as to targeted repair of fractured SEI. Due to the high thermal stability of polymerized D₃F, exothermic reaction between LiC_x and electrolyte is inhibited. As a result, the self-exothermic and TR trigger temperatures of pouch cell are increased from 159.6 and 194.2 °C to 300.5 and 329.7 °C. This work opens up a new avenue for designing functional additives to block initial exothermal reaction and inhibit TR in early stage.