By adding a CFRP sleeve to cylindrical battery cells, SWR can be prevented from occurring or propagating. (Image: NASA)

Innovators at NASA Johnson Space Center have developed a carbon fiber reinforced polymer (CFRP) sleeve, that, when fitted over a cylindrical Li-ion battery cell, can prevent cell-to-cell propagation by containing a thermal runaway (TR) event to the originating cell.

TR is caused by a battery cell short-circuiting and its inability to contain the resulting increase in pressure and temperature, which may lead to a sidewall rupture (SWR). Space flight and other industrial batteries frequently utilize multiple cells, such as the 18650, that are assembled into modules or battery packs and provide power to a variety of applications. A TR event can propagate to all the cells in a battery pack, escalating into a fire that can be catastrophic.

Previous battery designs have addressed SWR propagation by using aluminum or steel interstitial materials to prevent SWRs from directly impacting neighboring cells, but these materials were underperforming. During testing of 18650 battery cells, it was discovered that cells over 2.6Ah in capacity can have an undesirable failure mode in which the cell wall will rupture or breach during a TR event sending heat and eject into an undesirable direction.

TR is typically triggered when heat produced by the battery cells exothermic reaction leads to increased and escalating internal cell temperature, pressure, and boiling of the electrolytes. When internal cell pressure exceeds the cells safety relief mechanism, rupture or bursting can occur, initiating a cell-to-cell propagation that in turn results in a battery pack fire.

An engineer holds a spent test fixture attached to an 18650 Li-ion battery cell with an external carbon fiber reinforced polymer sleeve. Notice the sleeve intact, even after a thermal runaway event was induced in the battery cell. (Image: NASA)

By adding a CFRP sleeve to cylindrical battery cells, SWR can be prevented from occurring or propagating. In initial testing, there were no SWRs of a battery cell using a CFRP sleeve. This result is believed to be due in part to a unique characteristic of CFRP sleeves compared to other materials. Carbon fiber material has a negative coefficient of expansion and accordingly shrinks when heated, while steel and aluminum expand. The shrinking of the CFRP sleeve when heated compresses the cell located within it, significantly aiding in the prevention of SWR.

Use of CFRP sleeves for Li-ion cells provides multiple advantages over previous containment designs: increased hazard safety, lower mass, reduced cost, lack of conductivity, and manufacture with readily available materials. This technology can be implemented into other multiphysics battery safety models to guide the design of the next generation of battery cells and battery packs.

NASA is actively seeking licensees to commercialize this technology. Please contact NASA’s Licensing Concierge at This email address is being protected from spambots. You need JavaScript enabled to view it. or call at 202-358-7432 to initiate licensing discussions. For more information, visit here .