Electrochemical Abuse‐Driven Thermal Runaway in Lithium‐Ion Batteries: Evolution From Beginning‐of‐Life to End‐of‐Life

Abstract Thermal runaway, driven by exothermic redox reactions in lithium‐ion batteries, poses a significant barrier to their widespread adoption. While studies typically attribute thermal runaway to mechanical, electrical, or thermal abuse, the impact of electrochemical abuse remains underexplored, despite its relevance in cells degraded through prolonged use. Electrochemical abuse induces complex phenomena within the cell, such as lithium plating, electrolyte consumption, and the reduction of active lithium content (commonly observed as SoC shift), making it challenging to systematically understand how each factor affects thermal runaway. This study elucidates the differences in thermal runaway mechanisms between beginning‐of‐life (BoL) and end‐of‐life (EoL) cells using synchrotron‐based high‐temperature X‐ray diffraction, differential scanning calorimetry, and simultaneous thermal analyzer‐mass spectrometer. Furthermore, the specific impacts of lithium plating, electrolyte consumption, and SoC shift on EoL cells are systematically examined through controlled experiments. The results reveal that lithium plating lowers the thermal runaway initiation temperature by providing a reactive lithium source on the anode surface, while SoC shift generally reduces the overall thermal energy output. Electrolyte consumption does not significantly affect the total energy released during thermal runaway but delays exothermic reactions to higher temperatures. These findings demonstrate how thermal runaway behavior evolves over the lifespan of EV batteries.