Multistage Thermally Responsive Aerogel for Full‐Cycle Thermal Protection in Battery Modules to Prevent Thermal Runaway Propagation

Thermal runaway propagation (TRP) remains a critical safety challenge for lithium‐ion batteries (LIBs). However, traditional thermal protection materials cannot address the coupled hazards of heat, flames, and explosion‐induced mechanical impact during TR. Herein, a multistage thermal response aerogel strategy for full‐cycle TR protection was designed. During the controllable stage, the aerogel releases water vapor, which not only reduces the theoretical oxygen mole fraction to 4.07% but also enables early warning through changes in local humidity. During the uncontrollable stage, Co‐BDC‐assisted decomposition sustains the evolution of flame‐retardant gases, enabling prolonged flame suppression. Meanwhile, an in situ ceramization reaction is triggered, generating a dense ceramic layer on the aerogel surface. Together with sustained gas‐phase flame suppression, this condensed‐phase ceramic barrier effectively suppresses flame propagation. The sandwich‐like porous structure of the aerogel creates a tortuous heat‐transfer pathway, suppressing heat transfer. Furthermore, in situ ceramization enhances the compressive strength of the aerogel from 1.25 to 4.5 MPa, enabling resistance against explosion‐induced mechanical impact during TR. TRP experiments conducted on different battery modules confirmed that the aerogel effectively suppresses TRP. This study demonstrates a strategy for thermal protection materials that is tailored to the stages of TR, ensuring the operational safety of battery modules.