South Africa-born US innovator and entrepreneur Elon Musk has asserted that the type and layout of lithium ion batteries used by Boeing in its revolutionary 787 Dreamliner is “inherently unsafe”. Musk, founder, CEO and chief designer of rocket and spacecraft company SpaceX and CEO and head of product design of electric car company Tesla Motors, was communicating with British aerospace journal Flight International.
 
All Boeing 787s have been grounded worldwide as a result of battery problems experienced in early January. This involved a battery explosion on a Japan Air Lines aircraft and a battery overheating and spraying burning electrolytes in a compartment beneath the cockpit of an All Nippon Airways 787. These failures are now being investigated by Japanese and US air safety authorities.

Boeing uses lithium ion batteries that are powered by lithium cobalt oxide. These have some of the highest energy densities of any lithium ion batteries but are also amongst the most vulnerable to “thermal runaway” (overheating that can result in a fire). Tesla uses the same category of batteries in its cars, while a version has also been developed for use in SpaceX’s Falcon 9 space rocket.

“Unfortunately,” Musk told the UK magazine, “the pack architecture supplied to Boeing is inherently unsafe. Large cells without enough space between them to isolate against the cell-to-cell thermal domino effect means it is simply a matter of time before there are more incidents of this nature.”

The batteries used by Boeing in the 787 each have eight of these, each rated at 3.7 V. In contrast, Tesla uses batteries with thousands of small cells, each separated from all the others to stop thermal runaway or fire in one affecting any of the others.

“Moreover, when thermal runaway occurs with a big cell, a proportionately larger amount of energy is released and it is very difficult to prevent that energy from then heating up the neighbouring cells and causing a domino effect that results in the entire pack catching fire,” he affirmed. “I think there is a fundamental safety issue with the architecture of a pack with large cells. It is much harder to maintain an even temperature in a large cell as the distance from the centre of the cell to the edge is much greater, which increases the risk of thermal runaway.”