Rethinking Battery Safety: Unveiling Aluminum Propellant‐Like Reactions During Thermal Runaway and Developing Protective Solutions

ABSTRACT Battery safety remains a critical challenge in the large‐scale deployment of lithium‐ion batteries. While thermal runaway is typically attributed to exothermic reactions involving electrode materials and electrolytes, the contribution of current collectors has been largely overlooked. Here, we demonstrate that the conventionally presumed inert aluminum (Al) current collector engages in intense exothermic reactions with various cathode materials at temperatures exceeding 600°C. This reactivity is catalyzed by fluorides, which disrupt the Al passivation layer, resembling combustion mechanisms observed in Al‐based rocket propellants. The specific heat release from Al oxidation (−22 to −33 kJ g −1 ) is nearly twice that of the electrolyte (−12 to −16 kJ g −1 ). Considering that the Al mass is approximately half that of the electrolyte, its theoretical thermal contribution during thermal runaway is comparable to that of the electrolyte. Employing fluorine‐free electrolytes can suppress the propellant‐like reaction. Together with flame‐retardant strategies, the total heat release during thermal runaway can be further reduced, with the measured peak temperatures around pouch cells being effectively suppressed below 400°C. This work uncovers a pervasive yet previously underappreciated high‐energy reaction in batteries and offers new design strategies for improving thermal safety.