Fire-safe lithium-ion battery design survives nail puncture and prevents thermal runaway
Traditional lithium-ion batteries, which power a wide range of electronic devices from cars to smartwatches, pose a significant fire risk. When damaged, overcharged, or defective, they can undergo thermal runaway — a dangerous event in which internal components break down and release extreme heat. In a typical battery, this can cause temperatures to spike by over 500 °C, leading to fires and explosions.
Now, a team of researchers in China, primarily from the Chinese University of Hong Kong, has developed a new battery design that mitigates this risk. In a study — published in the journal Nature — the team detailed the new design and test results. When penetrated with a nail, the lithium-ion battery made with this design saw a temperature rise of about 3.5 °C and remained stable. As for the battery with conventional electrolytes, a temperature spike of 555.2 °C, explosion, and fire were recorded.
The team was only able to make this breakthrough after identifying the culprit — ion association. In conventional batteries, the way lithium ions and negative ions group together in the electrolyte is good for forming a protective layer called the solid electrolyte interphase (SEI), which is vital for a long cycle life. However, the researchers discovered this same ion association also lowers the temperature at which thermal runaway begins by approximately 94 °C, making the battery far less safe.
To solve this trade-off, the team developed what they call a “solvent-relay strategy.” They engineered a new electrolyte that behaves differently at different temperatures. At room-temperature conditions, it promotes the ion association needed for good SEI formation. But at elevated temperatures — like those from damage — a specific solvent called lithium bis(fluorosulfonyl)imide steps in, bonding with the lithium and promoting ion dissociation. This action inhibits the dangerous anion bonds that would otherwise lead to heat release.
The design proved to be both safe and durable. The cells designed with their new strategy also demonstrated an exceptional cycle life, retaining approximately 81.9% of their capacity after 1,000 cycles.
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