Ceramifiable foam composite confines thermal runaway in lab battery module tests

From ESS News

Thermal runaway propagation — the cascade in which a failing cell triggers sequential failure across an entire battery module – is now a primary safety hazard in utility-scale lithium-ion battery energy storage systems. Gas jets ejected during runaway events reach core temperatures of 800 C to 1,200 C and ejection velocities exceeding 200 meters per second. Conventional passive insulation materials fail under these conditions: organic foams collapse above 300 C, while inorganic fiber materials disintegrate under high-velocity jet impingement.

Researchers at China University of Petroleum-Beijing and the China Academy of Safety Science and Technology have developed a gradient-laminated ceramifiable silicone foam composite that addresses both failure modes. The material integrates a polydimethylsiloxane foam matrix with an embedded glass fiber fabric skeleton and a multiscale filler system including ammonium polyphosphate, zinc borate, kaolin, and silica aerogel.

Under normal operating conditions the composite remains flexible and elastic, maintaining stable mechanical performance from minus 40 C to 300 C and retaining 93% residual stress after 1,000 compression cycles. Under fire exposure the fillers activate a multi-step ceramization process: flame retardants release inert gases and promote char formation, while kaolin and silica aerogel undergo liquid-phase sintering above 600 C to generate a dense ceramic barrier. The embedded glass fiber fabric resists perforation by high-pressure gas jets even after the foam surface has been compromised.

In cone calorimetry testing the composite reduced total heat release by 54.4% and smoke production by 87.9% relative to plain silicone foam. Under a butane flame generating approximately 1,100 C, the material maintained structural integrity for more than 30 minutes with rear-surface temperature stabilizing at 97.1 C. Thermal conductivity was measured at 0.046 W per meter per kelvin, approximately 50% lower than unmodified silicone foam. The material achieved a limiting oxygen index of 33.5% and passed the UL-94 V-0 flammability rating.

Battery module performance was evaluated in a controlled three-cell configuration using commercial 37 Ah prismatic cells. Without insulation, complete propagation across all three cells occurred within seconds of the first cell entering runaway. With conventional 3 mm silicone foam, propagation was delayed but not prevented. With 3 mm of the ceramifiable composite, thermal runaway was contained to the initiating cell in this test configuration: the adjacent cell’s front surface reached 167.1 C but did not cross the runaway threshold.

Total mass loss in the ceramifiable composite test was 255.4 grams, compared with 796.3 grams in the conventional silicone foam test, consistent with single-cell containment. In a separate comparative test using a commercial aerogel blanket – conducted by the same research team – single-cell containment was also achieved, though the adjacent cell’s front surface reached a slightly higher temperature of 181.1 C. The paper notes that the composite’s 3 mm profile preserves volumetric energy density of battery modules and that its fabrication process is compatible with industrial roll-to-roll manufacturing.

The scientists published their study, “Constructing Intrinsically Safe Lithium-Ion Battery Energy Storage via Gradient-Laminated Ceramifiable Silicone Foams,” in Nano-Micro Letters. The research was led by Prof. Congling Shi of the China Academy of Safety Science and Technology and Prof. Laibin Zhang of China University of Petroleum-Beijing, with co-authors Shuilai Qiu and Jingyao Xu.