In a study published in PNAS, Prof. ZHANG Ying, Prof. GUO Yuguo, and Prof. BAI Chunli from the Institute of Chemistry of the Chinese Academy of Sciences (ICCAS) have proposed a novel smart gas management strategy which constructs flame-retardant interfaces (FRIs) that completely prevent explosions in high-energy lithium-metal batteries. This study marks for the first time that thermal runaway has been fully suppressed under thermal abuse conditions.

Lithium (Li) metal batteries offer high energy density (>400 Wh/kg) for electric vehicles and grid storage but face significant safety challenges. At the anode, the reduction of organic carbonate-based electrolytes generates flammable gases (e.g., H₂, CH₄), and during overheating, these gases at the anode migrate and react with oxygen released from nickel-rich cathodes like NCM811, triggering explosive chain reactions that can exceed 1,000 °C within minutes.

Traditional solutions to these challenges focus solely on electrolyte additives or cathode coatings, failing to address the synergistic gas dynamics that amplify thermal runaway. In this study, researchers synthesized a phosphonate-based flame-retardant polymer (FRP) and embedded it directly into the cathode structure via ultraviolet-assisted electrophoretic deposition.

Through multi-scale experimental characterization combining time-of-flight secondary ion mass spectrometry (TOF-SIMS) for interface mapping, evolved gas analysis-mass spectrometry (EGA-MS) for cathode decomposition tracking, and accelerated rate calorimetry (ARC) for full-cell safety validation, researchers constructed continuous FRIs that function as "intelligent firewalls."

A critical thermal threshold was identified at approximately 100 °C, at which FRIs initiate a dual-protection mechanism. First, through lattice stabilization, they suppress oxygen release from the cathode by 49%, effectively reducing the fuel available for combustion. Second, the FRP decomposes to release [PO]· radicals which diffuse to the anode where they quench free-radical chain reactions and drastically reduce flammable gas production by 63%.

In 0.6-Ah Li||NCM811 pouch cells under thermal abuse conditions, FRIs eliminated explosions and reduced peak temperatures from 1,038 °C to 220 °C. The maximum self-heating rate plummeted 10,000-fold (from 43,300 °C/min to 1.1 °C/min), while flammable hydrocarbons in gas emissions dropped from 62% to 19%, replaced by inert CO₂. The prototype pouch cell showed no fire or explosion during the ARC test.

The micro-mechanisms revealed in this study provide a blueprint for next-generation battery designs. "FRIs transform gas management from passive containment to active prevention," said Prof. BAI. This work provides a promising pathway toward fire-safe Li metal batteries for electric vehicles and other energy storage applications.