Prof. ZHANG Ying, Prof. GUO Yuguo, and Prof. BAI Chunli at the Institute of Chemistry, Chinese Academy of Sciences (ICCAS), have pioneered flame-retardant interfaces (FRIs) that completely prevent explosions in high-energy lithium-metal batteries. This breakthrough, achieved through a novel "smart gas management" strategy, marks the first time thermal runaway has been fully suppressed under thermal abuse conditions,

Lithium-metal batteries offer exceptional energy density (>400 Wh/kg) for electric vehicles and grid storage but face catastrophic safety risks. During overheating, flammable gases (e.g., H₂, CH₄) generated 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 focused solely on electrolyte additives or cathode coatings, failing to address the synergistic gas dynamics that amplify thermal runaway.To tackle this, the team 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, they engineered 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 testing, 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 here provide a blueprint for next-generation battery designs. "FRIs transform gas management from passive containment to active prevention," says Prof. BAI. "This technology holds significant industrial application prospects—compatible with existing electrode manufacturing—and can extend to electric vehicles and even electric aircraft fields."

Optical images of 0.6-Ah Li||NCM811 pouch cells after thermal abuse testing: without FRIs (left, catastrophic explosion) versus with FRIs (right, mild swelling only). (Image by ZHANG Ying)

This study was published in PNAS.

Contact Information

Prof. ZHANG Ying, GUO Yu-Guo, BAI Chunli

Institute of Chemistry, Chinese Academy of Sciences (ICCAS)

Email: yzhang@iccas.ac.cn, ygguo@iccas.ac.cn, clbai@cas.cn