Full-Dimensional Analysis of Gaseous Products to Unlocking In Depth Thermal Runaway Mechanism of Li-Ion Batteries.

In this study, state-of-the-art on-line pyrolysis MS (OP-MS) equipped with temperature-controlled cold trap and on-line pyrolysis GC/MS (OP-GC/MS) injected through high-vacuum negative-pressure gas sampling (HVNPGS) programming are originally designed/constructed to identify/quantify the dynamic change of common permanent gases and micromolecule organics from the anode/cathode-electrolyte reactions during thermal runaway (TR) process, and corresponding TR mechanisms are further perfected/complemented. On LiC anode side, solid electrolyte interphase (SEI) would undergo continuous decomposition and regeneration, and the R-H (e.g., HF, ROH, etc.) species derived from electrolyte decomposition would continue to react with Li/LiC to generate H. Up to above 200 °C, the O would release from the charged NCM cathode and organic radicals would be consumed/oxidized by evolved O to form CO, HO, and more corrosive HF. On the contrary, charged LFP cathode does not present obvious O evolution during heating process and the unreacted flammable/toxic organic species would exit in the form of high temperature/high-pressure (HT/HP) vapors within batteries, indicating higher potential safety risks. Additionally, the in depth understanding of the TR mechanism outlined above provides a clear direction for the design/modification of thermostable electrodes and non-flammable electrolytes for safer batteries.