- Internal battery firewall stops overheating before fires start under fault conditions
- Ampere-hour sodium ion cells demonstrate complete suppression of thermal runaway reactions
- Triple safety system improves stability without reducing energy output performance
One of the biggest risks of modern batteries is overheating, which can lead to fires, but researchers at the Chinese Academy of Sciences (CAS) claim to have developed a sodium-ion battery material that forms a solid internal barrier as temperatures rise, stopping fires before they start.
The dangerous chain reaction it addresses is known as thermal runaway, and it occurs when heat inside a battery builds up faster than it can escape. Once it starts, the temperature rises rapidly and can lead to gas leakage, fire or explosions.
This failure mode remains one of the biggest safety concerns for electric vehicles and grid-scale storage systems. Preventing the reaction altogether, rather than trying to limit it afterwards, has been a major goal for battery developers.
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A three-part structure
Electric vehicles are often compared to internal combustion engine (ICE) vehicles, which carry gasoline that can ignite if damaged. A battery that stops overheating before it spreads can reduce the risk of fire.
The Chinese research team built what it calls a polymerizable non-flammable electrolyte, or PNE. This liquid changes to a dense solid when the temperature exceeds approx. 302°F (150°C).
This transformation creates an internal layer that blocks heat movement between battery components. In other words, the battery builds its own firewall the moment the overheating starts.
Researchers described the chemistry behind the system in their work published in Nature. “Here, we propose a polymerizable and nonflammable electrolyte that exploits the synergistic anion-cation solvation effect and undergoes thermally triggered polymerization,” they said.
The safety design works as a three-part structure that supports thermal stability, interface stability and physical separation inside the battery. Each layer plays a role in preventing reactions from spreading as the temperature rises.
Testing was conducted using a 3.5 Ah cylindrical sodium-ion battery, a capacity considered meaningful beyond small laboratory samples.
The researchers reported that this marked the first demonstration of complete thermal runaway suppression in ampere-hour-scale sodium-ion cells.
During nail penetration testing, the method typically used to simulate internal short circuits, the battery produced no smoke, fire or explosion. The cell also remained stable at temperatures reaching 572°F (300°C).
Researchers reported that safety gains also did not reduce performance. The battery achieved an energy density of 211Wh/kg, placing it within the expected range for advanced sodium ion systems.
Reliable operation was recorded across temperatures from -40°F to 140°F, covering conditions from deep winter to extreme summer heat. Voltage stability above 4.3V was also maintained during testing.
The researchers say the materials used in the system are already common in industrial production, which could simplify scaling if the technology reaches the commercial production stage.
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