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Li-ion battery with built-in flame retardant could stop battery fires

Stanford university battery automatically extinguishes its own flames.

Sebastian AnthonyThe PVDF-HFP fibres, which contain the flame retardant TPP.
The electrochemical masterminds at Stanford University have created a lithium-ion battery with built-in flame suppression. When the battery reaches a critical temperature (160 degrees Celsius in this case), an integrated flame retardant is released, extinguishing any flames within 0.4 seconds. Importantly, the addition of an integrated flame retardant doesn't reduce the performance of the battery.
As you may have surmised from the recent exploding Galaxy Note 7 fracas, one of the few weaknesses of lithium-ion batteries is that they contain a highly flammable electrolyte. If a Li-ion battery undergoes thermal runaway—due to physical damage, or perhaps a fault in the charging/discharging circuit—the result is usually a very big fire, sometimes followed by an explosion.
One solution, discovered by Stanford University researchers, is to create a new separator—the semipermeable membrane between the positive and negative sides of the battery—that contains a flame retardant. Usually the separator is a boring polymer like polyethylene, the world's most commonly used plastic. The new separator consists of fibrous threads of triphenyl phosphate (TPP), a common flame retardant, with a shell of another polymer (PVDF-HFP). The polymer shell prevents the TPP from seeping into the electrolyte, which would reduce the battery's performance.

Digital photographs showing the flammability of the TPP@PVDF-HFP separator wetted by the electrolyte. The respective times, counted from the time when the electrolyte started to burn, are indicated in each picture. The diameter of the separator is 1.6 cm.
Digital photographs showing the flammability of the TPP@PVDF-HFP separator wetted by the electrolyte. The respective times, counted from the time when the electrolyte started to burn, are indicated in each picture. The diameter of the separator is 1.6 cm.
Science Advances

When the separator hits 160 degrees Celsius, the polymer melts, abruptly releasing the TPP into the electrolyte and extinguishing the combustion. In the image above, the separator is doused with electrolyte, set on fire, and then the TPP is released within 0.4 seconds, quelling the flame.
The researchers note that the new separator has been successfully trialled in a coin cell, but that further testing needs to be done, to see if the integrated flame retardant is still effective when larger cells are crushed, pierced, or electrically abused. Otherwise, the data looks good: the new separator is flexible, strong, and doesn't seem to affect long-term performance of the battery.
In somewhat related news, Samsung said this morning that it will announce the results of its internal investigation into the exploding Galaxy Note 7 next Monday, January 23.
Science Advances, 2017. DOI: 10.1126/sciadv.1601978
This post originated on Ars Technica UK
Listing image by Crushader
Li-ion battery with built-in flame retardant could stop battery fires Reviewed by Chidinma C Amadi on 11:32 PM Rating: 5

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