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Material Developed to Prevent Li-Ion Battery Fires

Membrane resisting flame

The aramid-nanofiber membrane is stable at high temperatures and resists igniting, even when subjected to a direct flame. (Joseph Xu, University of Michigan)

28 January 2015. Materials scientists and engineers at University of Michigan designed a new material to better protect lithium-ion batteries from starting fires like the kind on Boeing 787 Dreamliners. The team from the lab of engineering professor Nicholas Kotov published its findings yesterday in the journal Nature Communications (paid subscription required).

Kotov and first author Siu-On Tung are principals in the spin-off company Elegus Technologies, formed to commercialize the technology. Tung is one of the inventors of the material and the company’s chief technologist.

A Japan Airlines 787 Dreamliner aircraft caught fire at Logan Airport in Boston in January 2013 that had two lithium-ion batteries to drive on-board electronics. An investigation by the National Transportation Safety Board revealed a short circuit in one of the battery’s eight cells started a cascading set of failures that resulted in a fire consuming the battery pack. NTSB recommended better management of new technology and tighter inspections, but Boeing also introduced better protections for battery packs, including steel casing and tubes to vent exhausts to the aircraft’s exterior.

Kotov and colleagues seek to improve the battery by inserting a stronger barrier between the electrodes that prevents the build-up of lithium atoms into extensions resembling tree branches called dendrites. If the dendrites poke through the membrane separating the electrodes, they can form an alternative connection that short-circuits the battery, which is believed to have caused the Dreamliner fires.

The Michigan team’s approach is to place a stronger barrier between the electrodes that prevents dendrites from puncturing the barrier, yet still allows for the flow of electrons through the intended circuit. The solution uses nanoscale aramid fibers configured to prevent dendrite punctures, yet still enable electrons to cross.

Aramid is a synthetic polymer with molecules in rigid chains linked by strong hydrogen bonds that efficiently transfer mechanical stress. Probably the most well-known application of aramids is Kevlar, a material made by DuPont used in bullet-proof vests.

The researchers created a membrane from aramid nanofibers arrayed in layers. The thin layers stretch out the chains in the aramid polymer, which the authors say improves conductivity between the battery’s electrodes. At the same time, the pores in the membrane devised at Michigan are 15 to 20 nanometers in diameter, smaller than the tips of dendrites, measured at 20 to 50 nanometers, as well as the few hundred nanometer pores in a typical Li-Ion battery.

Tests of the membrane show it restricts the growth of dendrites and keeps them from poking through creating conditions for a short circuit, while exhibiting the conductivity needed for the battery to function. The aramid fibers are also more stable at high temperatures, making them less likely to ignite. In addition, the membrane is thinner than conventional Li-Ion batteries, which takes up less space and can result in smaller batteries or more power for their size.

Elegus Technologies, the company formed by Tung and associates at Michigan, is taking the lab’s new membranes for lithium-ion batteries to market, and expect to begin commercial-scale production by the end of 2016. The university says it already received requests from 30 companies for samples of the material.

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