In Situ Generation of Gel Foam via Heat‐Accelerated Calcium Ion Release From Nano‐CaCO 3 for Lithium‐Ion Battery Fire Suppression and Prevention

ABSTRACT Thermal runaway and its propagation in lithium‐ion battery packs pose significant safety risks to energy storage systems. While complete immersion in water‐based agents is an effective suppression strategy, conventional agents often fail to achieve sustained battery encapsulation because of low viscosity and rapid runoff. In this study, we report a thermally accelerated in situ crosslinking strategy to create an alginate gel foam for excellent battery fire suppression and propagation prevention. Our approach utilizes nano‐CaCO 3 as a dormant calcium ion source and δ‐gluconolactone (GDL) as a slow acidifier. At ambient temperature, the extremely low solubility of nano‐CaCO 3 results in slow Ca 2+ release in aqueous solution, with the mixture maintaining low viscosity and excellent foamability. After exposure to battery fire, GDL hydrolysis is accelerated, causing rapid nano‐CaCO 3 dissociation, Ca 2+ release, and, subsequently, rapid ionic crosslinking of the alginate, which transforms the aqueous foam into a stable, adhesive gel foam. In full‐scale tests, we determined that this gel foam extinguishes single‐cell fires rapidly and significantly inhibits thermal runaway propagation (TRP) in multi‐cell modules, outperforming water mist, water spray, and commercial aqueous film‐forming foam (AFFF). This stimulus‐responsive alginate gel foam offers a promising strategy for increasing the safety of lithium‐ion batteries.