Safer Li-Ion Batteries using Kevlar membranes
Shawn Wasserman posted on January 28, 2015 |
New Kevlar membrane could save lives, prevent airline disasters, reduce battery size and increase fi...

Bulletproof vest technology is now being used to produce safer batteries. University of Michigan (U-M) engineers have developed a way to use Kevlar membranes to prevent battery fires, such as the one that affected the Boeing 787 Dreamliner in 2013.

The membrane is made from Kevlar nanofibers and acts as a barrier between the electrodes in a lithium-ion battery. The membrane helps to prevent the growth of metal tendrils in the battery that can short circuit the system and even lead to fire.

Engineering Professor Nicholas Kotov explained, "Unlike other ultra-strong materials such as carbon nanotubes, Kevlar is an insulator … This property is perfect for separators that need to prevent shorting between two electrodes."

Like many electrochemical batteries, Lithium-ion batteries pass ions from one electrode to another. The circuit is completed as the electrons pass through the load and meet at the other electrode. The membrane acts as a way to prevent backward flow in the battery.

However, if the gaps in the membrane are big enough, the lithium will build up in fern-like structures called dendrites. These structures can puncture the membrane and eventually reach the electrode. Now the electrons will be able to flow through the battery and short the system. It is believed that this process caused the fire that grounded the 2013 787 Dreamliner.

Elegus Technologies was created by the U-M research team to bring this technology to market. They hope that mass production will bring Kevlar batteries to market in late 2016.

According to Siu On Tung, Kotov’s grad student and CTO of Elegus, "The fern shape is particularly difficult to stop because of its nanoscale tip … It was very important that the fibers formed smaller pores than the tip size."

This is where the Kevlar membrane shines, with a pore diameter size around 15 to 20 nanometers it is smaller than traditional membranes by a factor of 10 or larger. Thus, it’s pores are small enough to block the 20-50 nanometer dendrite tips, but large enough for the lithium ions to pass. What’s more, the Kevlar membrane is more fire resistant than other membranes, which should help create even safer batteries.

Tung also mentioned that the membrane was produced by layering fibers on a thin sheet. This ensures the molecule chains are stretched, allowing lithium-ions to pass between the electrodes. The research team is currently looking to increase the lithium-ion flow through the battery for faster charging and release of energy.

Dan VanderLey, Elegus founder and U-M Entrepreneur Master said, "The special feature of this material is we can make it very thin, so we can get more energy into the same battery cell size, or we can shrink the cell size … We've seen a lot of interest from people looking to make thinner products." He isn’t kidding, either, as more than thirty companies have requested samples of the membrane.

For more information on the Kevlar membrane check out this paper.

Source University of Michigan.

 

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