A research team at Stanford University has designed a lithium-ion battery that releases a flame-retardant when the device gets too hot.
The researchers explain that lithium-ion batteries are considered to be one of the most promising power sources of electric vehicles because of their high specific energy densities, stable cycling performance, and other related qualities.
However, as energy densities of batteries increase, safety problems remain an issue because highly flammable liquid organic electrolytes are used in lithium-ion batteries. A short circuit could cause an increase in temperature, eventually causing a fire or explosion.
To solve this problem, researchers tried replacing the existing flammable electrolyte with non-flammable ones, and using flame-retardant separators, among others. However, researchers say the risk of battery fire still exists and battery performance is usually sacrificed when these methods are used.
To get around this problem, the Stanford researchers added flame-retardant triphenyl phosphate (TPP) to fibres that surround the battery. If the battery heats up, the fibres will melt and release the TPP.
"The encapsulation of a flame-retardant inside a protective polymer shell has prevented direct dissolution of the retardant agent into the electrolyte, which would otherwise have negative effects on battery performance," states the research abstract.
In tests, the researchers found it took 0.4 seconds to extinguish all flames.
It is not yet clear if and when this technology will be included in designs of future products. However, it comes at a time when customers are wary of explosive devices due to Samsung's premium phablet Note 7 catching fire last year.
When the first Samsung Galaxy Note 7 exploded in early September 2016, Samsung said this was due to the lithium polymer battery manufacturing process. It issued a recall and offered to replace the devices. Then the replacement phones started to heat up and smoke, and Samsung decided to cancel the entire product line.
Not enough space
In December last year, tech firm Instrumental issued a report which said aggressive design caused the Note 7 battery explosions. The firm found the design of the smartphone compresses the battery, even during normal operation.
The firm explained: "When batteries are charged and discharged, chemical processes cause the lithium to migrate and the battery will mechanically swell. Any battery engineer will tell you that it's necessary to leave some percentage of ceiling above the battery (roughly 10% as the battery will expand over time)."
The two-month-old Samsung Note 7 Instrumental tested had a 5.2mm thick battery resting in a 5.2mm deep pocket.
This is important, noted the company, because the Note 7's lithium-polymer battery comprises four layers: a lithium cobalt oxide positive layer, a negative graphite layer, and two electrolyte-soaked polymer separator layers. If the positive and negative layers touch, more heat and energy will flow directly into the electrolyte, which normally results in an explosion.
Therefore, "compressing the battery puts pressure on those critical polymer separator layers that keep the battery safe".
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