Thermal Runaway Mechanism in Ni‐Rich Cathode Full Cells of Lithium‐Ion Batteries: The Role of Multidirectional Crosstalk

Abstract Crosstalk, the exchange of chemical species between battery electrodes, significantly accelerates thermal runaway (TR) of lithium‐ion batteries. To date, the understanding of their main mechanisms has centered on single‐directional crosstalk of oxygen (O₂) gas from the cathode to the anode, underestimating the exothermic reactions during TR. However, the role of multidirectional crosstalk in steering additional exothermic reactions is yet to be elucidated due to the difficulties of correlative in situ analyses of full cells. Herein, the way in which such crosstalk triggers self‐amplifying feedback is elucidated that dramatically exacerbates TR within enclosed full cells, by employing synchrotron‐based high‐temperature X‐ray diffraction, mass spectrometry, and calorimetry. These findings reveal that ethylene (C₂H₄) gas generated at the anode promotes O₂ evolution at the cathode. This O₂ then returns to the anode, further promoting additional C₂H₄ formation and creating a self‐amplifying loop, thereby intensifying TR. Furthermore, CO₂, traditionally viewed as an extinguishing gas, engages in the crosstalk by interacting with lithium at the anode to form Li₂CO₃, thereby accelerating TR beyond prior expectations. These insights have led to develop an anode coating that impedes the formation of C₂H₄ and O₂, to effectively mitigate TR.