Safer lithium-ion battery design prevents thermal runaway that can cause fires - Engineering - Energy & Green Tech

Ion association promotes SEI formation while facilitating anion thermal decomposition. Credit: Nature Energy (2025). DOI: 10.1038/s41560-025-01888-5

Conventional lithium-ion batteries are known to present a fire risk, and can even cause explosions in certain cases. The widespread usage of lithium-ion batteries, in everything from electric vehicles to electric toothbrushes, makes lithium-ion battery fire risk mitigation a major priority. There is a great need for lithium-ion battery designs that balance long cycle life, high voltage, and safety.

The fire risk arises when lithium-ion batteries undergo some kind of physical damage, are overcharged or even when they have manufacturing defects. This causes thermal runaway when anions—or negatively charged ions—break their bonds with lithium and release heat. Conventional lithium-ion batteries can undergo a temperature change of over 500°C when this occurs.

However, researchers in China have now found a way to drastically reduce the heat released when lithium-ion batteries are damaged. Their study, published in Nature Energy, details the new design and the experimental results of nail penetration tests, in which the temperature rise was only around 3.5°C.

Videos showing nail penetration tests of 1.1 Ah graphite-NCM811 pouch cells using commercial electrolytes (1 M LiPF₆ in, 1:1 vol%) and GBF-D2 electrolyte. Credit: Nature Energy (2025). DOI: 10.1038/s41560-025-01888-5

The new design was made possible after the team found that ion association in electrolytes within the batteries was lowering the temperature at which thermal runaway occurred by around 94°C. They realized that replacing some of the solvent in the battery with a different material should lower the risk of thermal runaway by increasing the temperature that it begins at. This replacement would also still allow solid electrolyte interphase (SEI) formation at lower temperatures, which is a normal function of a lithium-ion battery.

And so, the researchers developed a "solvent-relay strategy" that promotes ion association at room temperature for SEI formation, but induces dissociation at high temperatures for safety. The new design involves a solvent called lithium bis(fluorosulfonyl)imide, which bonds with the lithium from the existing solvent only at higher temperatures, inhibiting the anion bonds that produce eventual thermal runaway.

The team tested out the new design in 1.1 Ah pouch cells by puncturing them with a nail—a common safety assessment test for lithium-ion batteries.

"This approach enabled 4.5 V graphite-NCM811 pouch cells (1.1 Ah) that exhibited an exceptional cycle life of 4,100 hours with approximately 81.9% capacity retention (1,000 cycles under 0.45 C). These ampere-hour-scale cells also demonstrated enhanced thermal stability, with a temperature increase of less than 3.5 °C during nail penetration tests, compared to 555.2 °C for cells with commercial electrolytes," the study authors write.

This new design is a clear leap forward for lithium-ion battery safety. Although some more testing is needed, these changes could be incorporated into lithium-ion batteries in the near future.

The study authors write, "This study elucidates the critical influence of ion association on thermal runaway and establishes an effective strategy to achieve prolonged cycle life, high cut-off voltage and enhanced safety in ampere-hour-level lithium-ion batteries."

by Krystal Kasal, Phys.org

edited by Gaby Clark, reviewed by Robert Egan 

Source: Safer lithium-ion battery design prevents thermal runaway that can cause fires