After nearly half a year stuck on the ground because of mysterious battery fires, the Dreamliner is flying again. To get the 787 back in the sky, Boeing added a set of FAA-approved retrofits to the plane’s lithium-ion batteries to prevent the kind of failures that occurred in January, when one battery caught fire and another failed during flight. Although engineers are still unsure what caused the cells to ignite, they do know the failures were a result of thermal runaway – in this case, an uncontrollable rise in pressure and temperature that occurred after a single cell in each battery short-circuited and caused the rest of the cells to overheat.
To make the batteries safer, engineers replaced their PVC insulation, which can handle up to 149 degrees, with phenolic glass laminate, a material resistant up to 480 degrees. They’ve also added titanium venting, so if a cell bursts, the electrolyte mix it lets out leaves the plane entirely. As both a safety measure of last resort and a way to keep oxygen levels too low for combustion, the batteries are encased in steel. The downside: the aircraft gains 68 kg, negating the lightweight benefit of a lithium-ion battery in the first place.
Steel box: A steel box keeps oxygen levels too low to allow for combustion
Cell isolation: Each cell is encased in electrical-isolation tape.
Cell separation: The cells are separated by ceramic spacers.
Vent line: Electrolytes generated by overheating are expelled via a vent line.