In a recent experiment, engineers did something that would usually cause a fire: they blasted a high-capacity battery with a 3,600°F propane torch. 

There was no explosion, no frantic hissing, or toxic plume. In fact, the moment the torch was clicked off, the flames simply vanished. 

This week, MIT spinoff PolyJoule, Inc., officially pulled the curtain back on its third-generation battery chemistry, a technology designed to “self-extinguish.”  While the rest of the industry spends billions trying to stop batteries from exploding, PolyJoule built one that refuses to even stay lit.

Self-extinguishing properties

Standard batteries — whether in a phone, Tesla, or a massive grid-storage farm — depend on metals like lithium, cobalt, or nickel. These metals are reactive and prone to “thermal runaway,” a terrifying domino effect where one overheating cell triggers a neighborhood-wide blaze. 

“Batteries shouldn’t start fires. Batteries shouldn’t spread fires. Batteries shouldn’t catch on fire,” said Eli Paster, PolyJoule’s co-founder and CEO. 

It’s a simple thesis, but one that the industry has struggled to solve. PolyJoule’s solution is organic. 

Inside the cell, the lithium-metal fire-trap has been replaced by an innovative duo: a conductive polymer cathode and a liquid salt electrolyte.

Instead of a metallic crystalline lattice, the battery uses conductive polymers to hold a charge.

To prove its resilience, the company released video footage of a full-size cell enduring a 3,600°F (1,982°C) propane torch blast directly to its internal components.

Despite the extreme heat and visible off-gassing, the battery refused to succumb to the flames. The moment the torch was removed, the fire instantly self-extinguished, demonstrating a level of thermal stability that other metal-based batteries simply cannot match.

“Materials that have a propensity to catch fire often contain reactive metals that spontaneously react with air and volatile liquids. The advantage of PolyJoule’s batteries is that they have neither,” said Timothy Swager, the John D. MacArthur Professor of Chemistry at the Massachusetts Institute of Technology and a co-founder of PolyJoule.

The 10x leap

This third-gen chemistry delivers a 10-fold increase in energy density over its first iteration. It also has a lifespan of more than 10,000 cycles.

Overall, the chemistry eliminates the thermal runaway risks, dendrite formation, and complex cooling requirements that plague lithium-ion systems. 

Interestingly, the technology eliminates bulky cooling systems and leverages a domestic supply chain.

This shift from crystalline metallic structures to a stable liquid salt and polymer design offers a simpler, domestically sourced solution to the industry’s biggest issues: safety, supply chain volatility, and operational complexity.

As the world sprints toward a greener grid, the demand for stationary storage is skyrocketing. But as these installations move closer to homes and hospitals, mostly safe isn’t good enough.

“PolyJoule has created a product that can safely be put inside homes and businesses, using non-flammable conducting polymers and a liquid salt electrolyte that has a vapor pressure a billion times lower than that of the electrolytes used in Li-ion batteries,” Swager added. 

PolyJoule is positioning its technology not just as a green alternative, but as a peace of mind alternative.