Kevlar Could Mean Safer, Slimmer Batteries

The latest idea for making slimmer and/or more powerful batteries uses Kevlar, the material from bullet-proof vests.

University of Michigan researchers believe Kevlar could reduce the likelihood of batteries shorting out, something that not only makes them useless but risks a fire or explosion. They point to such problems grounding all Boeing 787 Dreamliner planes for three months back in 2013.

The researchers are looking at lithium-ion batteries, which use alternating layers of electrodes and an insulating membrane, allowing the battery to control the path taken by lithium ions.

Membranes have tiny holes that in principle are too small to let more than a single ion pass through. The problem is that lithium ions can build themselves into a structure called a dendrite that is similar in shape to a fern. In effect that focuses the force on the tip of the dendrite, which can fit into even a small hole in the membrane and work its way through, widening the hole until it forms a pathway between the electrodes. That creates a short circuit and a fire risk.

Using Kevlar for the membrane brings three main benefits:

• It’s high strength-to-thickness ratio allowed the researcher to build a membrane made of multiple layers, in turn allowing much smaller holes. The Kevlar membrane has holes of 15 to 20 nanometers, while a dendrite tip is usually 20 to 50 nanometers.
• Even with this design, the membrane is still extremely thin. That gives the option of creating a thinner battery with the same capacity, or a higher capacity battery of the same size.
• Kevlar is notably heat-resistant. That means that if a short circuit does occur, there’s less risk of it leading to fire or explosion.

The researchers have formed their own business, Elegus Technologies, with the intention of starting mass production by the end of next year. They say 30 companies have already requested samples of the membrane.